Trying to Select Destination for Installation

You are going about this the wrong way. The error is popping up because you are trying to install El Capitan on a volume running 10.13.6 - your startup volume. What you should do is the following:

Internet/Network Recovery of El Capitan or Later on a Clean Disk

     If possible back up your files before proceeding.

1. Restart the computer. Immediately, at or before the chime, hold down the (Command-Option-Shift-R) keys until a globe appears.
2. The Utility Menu will appear in from 5-20 minutes. Be patient.
3. Select Disk Utility and click on the Continue button.
4. When Disk Utility loads select the target drive (out-dented entry w/type and size) from the side list.
5. Click on the Erase button in Disk Utility's toolbar. A panel will drop down.
6. Set the partition scheme to GUID.
7. Set the Format type to APFS (SSDs, only if installing Mojave or Catalina ) or Mac OS Extended, (Journaled.)
8. Click on the Apply button, then click on the Done button when it activates.
9. Quit Disk Utility and return to the Utility Menu.
10. Select Install OS X and click on the Continue button.

This should install the version of OS X originally installed from the factory. You will need an active Internet connection; either Wi-Fi or Ethernet. The latter is preferable.

Do you have the Install OS X El Capitan.app in your Applications folder, good.

Do you have an 8GBs or larger USB stick, then use Disk Utility, click on View in

the menubar and select Show All Devices, select the USB in the left panel the Disk

not the indented Volume, now click Erase to format it as

Mac OS Extended (Journaled) on a GUID Partition Map, also make sure it

is called MyVolume. Excellent.

Click on this link, How to create a bootable installer for macOS – Apple Support

copy and paste the command for El Capitan, into Terminal, press Return.

When the bootable USB has been created, restart your mac while pressing

and holding the option/ alt key. This will boot your mac to the

Startup Manager, select the bootable USB and press Return.

When booted to the USB you will see a Utilities panel,

select Install OS X. Press Continue.

The main installer screen should show, follow the prompts

after a couple of screens you will get the chance to select

the destination disk, choose your internal, and continue with

the installation.

Mark,

You have some sort of odd problem. You installed Yosemite but it does not appear in Startup Disk preferences. Given your other difficulties with the computer, I wonder if the drive isn't the problem. Perhaps you could open Disk Utility and make a pic of the Disk Utility window to post here.

How to take a screenshot on your Mac

Capture, Save or Record Screenshots in Mac OS X - Help Desk Geek

OS X Screen Capture Shortcuts

(⌘⬆︎3) Command-Shift-3 Capture the screen to a file

(⌘⬆︎⌃3) Command-Shift-Control-3 Capture the screen to the Clipboard

(⌘⬆︎4) Command-Shift-4 Capture a selection to a file

(⌘⬆︎⌃4) Command-Shift-Control-4 Capture a selection to the Clipboard

(⌘⬆︎5) Command-Shift-5 Invoke new screen grabber

It's a puzzle to me. Why don't you just give in and boot from that external drive's Recovery HD (Command-R) and clone the 10.13.6 system to the drive and see how that goes?

Clone Lion Thru Yosemite using Restore Option of Disk Utility

1. Restart the computer. Immediately, at or before the chime, press and hold down the Command and R keys until the Apple logo and progress bar appear.
2. Wait until the Utility Menu appears.
3. Select Disk Utility from the main menu then press the Continue button.
4. Select the internal drive then click on the Erase button in the toolbar.
5. Set the Format type to Mac OS Extended, (Journaled) and click on the Apply button.
6. Select the destination volume from the left side list.
7. Click on the Restore button in the Disk Utility toolbar.
8. Select the destination volume from the left side list and drag it to the Destination entry field.
9. Select the source volume from the left side list and drag it to the Source entry field.
10. Double-check that you got it right, then click on the Restore button.

Destination means the Erased internal drive. Source means the External startup drive.

You have it formatted correctly. APFS is only available with Mojave or Catalina. I don't see anything in your screen shots that suggests why you are getting the error when installing El Capitan. Two things you might try:

Eject and disconnect the external drives.

Boot the computer into Safe Mode and try installing El Capitan again from safe mode.

Boot Into Safe Mode

1. If your Mac isn’t already shut down, then shut it down and wait at least 30 seconds before rebooting.
2. Immediately, at or before the chime, press and hold down the SHIFT key. 
3. Release the key after the Apple logo and progress bar appear.
4. Safe mode startup is much slower than normal startup, so be patient.
5. When the Login Screen appears enter your admin password. If you use automatic login, then this means you are in safe mode.

As many times as you have downloaded El Capitan, I can't believe it's a bad download. If you can spare one of the external drives, then you could erase it and try installing El Capitan on it. If you continue to get the same error, then I think the installer error means you need to install a later version of macOS. That is because your model should upgrade to Catalina.

It's part of Disk Utility where you are cloning a volume. It's the Restore button in the Disk Utility toolbar. Once you click on that button you will be presented with two fields on the right of the list. One is for the Source and the other for the Destination. Select the volume that corresponds to each and drag it into the field.

Here's part of one of your posted images of Disk Utility:

If this is the Disk Utility version in 10.13.6, then click on the Restore button you see in the toolbar. A panel will drop down that looks similar to this one:

The volume names you see may differ from mine. The Destination volume is the one you selected from the sidebar list. For mine that happens to be Macintosh HD. Select the Source volume from the dropdown menu labeled, Restore from:. Then click on the Restore button.

This different from my post because I thought you would be using the older version of Disk Utility. Here are new instructions:

Clone El Capitan and Later using Disk Utility

1. Restart the computer. Immediately, at or before the chime press and hold down the Command and R keys until the Apple logo and progress bar appear. Wait until the Utility Menu appears.
2. Select Disk Utility from the Utility Menu, then click on the Continue button.
3. Select the destination volume from the left side list - Macintosh HD.
4. Click on the Restore button from the Disk Utility toolbar. A panel will drop down.
5. Select the source volume from the dropdown menu in the panel - startup volume.
6. Double-check that you got it right, then click on the Restore button.

Yes, if the external drive has more data than there is space on the SSD, then the cloning will not work using Disk Utility. However, it is possible to install just the OS part of the source by using different backup software. If you use Carbon Copy Cloner, then you can select exactly what you want cloned. However, you will need to learn how to use different software for the process. CCC is a terrific piece of software, but it can be a little opaque at times. I suppose the other possibility would be to download the 10.13.6 installer to your external drive and try installing it on the internal SSD. If you want to give that a try, then boot from the external drive. Open the Terminal app in the Utilities folder, then copy and paste the following command line at the Terminal prompt:

softwareupdate --fetch-full-installer --full-installer-version 10.13.6

Press RETURN. This should begin the download process. The installer should download into your Downloads folder or to your Applications folder. I don't recall which one.

Run the installer. When the window appears to select the destination you should see a default disk icon. Below the icon is a link labeled, "Show all Disks." Click on that link, then select the internal SSD as the destination for the installation. Click the Install button. It will take about 30 minutes for the installation to be completed during which the computer may reboot several times which is normal.

When the installation is completed the computer should do one last reboot from the SSD.

Hello,

Were did you download the copy of macOS 10.11 El Capitan?

Some questions:

Did you install any third-party software before trying to upgrade to El Capitan?

Address TCP/IP filtering, firewall, or security software:

If you have TCP/IP filtering, firewall, or security software installed on your computer, try these steps.

1. 1. Configure or temporarily uninstall your security software.
   2. Be sure you have a working Internet connection. Try visiting www.apple.com or contact your Internet service provider for more help.
   3. Bypass your Internet router. Some routers might block iTunes from accessing the update server. If you're using a router that isn't manufactured by Apple, try the following:

• • • Disconnect from your wired or wireless router and use an Ethernet cable to connect your computer directly to your modem.
    • Restart your computer and modem. Contact your Internet service provider for instructions on using your modem.

After you confirm your Internet connection is working, try to update or restore your iOS or iPadOS device again.