I want to re-install a clean version of 10.15.7 on mu 2013 imac27

Hi Keithstoddart14,

As I think you stated, after this process is complete, you do not want to use Time Machine restore, as all issues will come back. Use your other backup with just your files. Below is how to do this process.

1. Sign out of your Apple ID in System Preferences > Apple ID > Overview > Sign Out
2. Shut down the Mac.
3. Turn on the Mac, and immediately press and hold Command + R until you see the Apple logo.
4. Once you are in macOS Recovery, verify you are connected to WiFi in the top right corner.
5. Go to Disk Utility.
6. Select "View" in the toolbar > "Show All Devices".
7. Select your main hard drive. This will either be "APPLE SSD...", "APPLE HDD...", or "Fusion Drive".
8. Click Erase, and input the following exactly: (If you cannot select erase on the main hard drive, erase the "Container".)
9. Name: Macintosh HD
10. Format: APFS
11. Scheme: GUID Partition Map (if shown)
12. Click Erase
13. Quit Disk Utility
14. Go to the reinstall macOS app.
15. Follow the prompts, and install on Macintosh HD.
16. Once done, setup your Mac, again, and once setup, drag and drop or copy your files back to the iMac.

Cheers,

Jack

Hi Keithstoddart14,

We see you're running into an issue with not being able to download files from any browser. We'd be happy to look into that with you, and help out however we can.

First, we'd advise checking out the available storage on the iMac. You can do that with the help of this page: How to free up storage space on your Mac

In addition to checking storage in the About This Mac screen, as noted in the above link, you can do so in Disk Utility (Finder > Applications > Utilities > Disk Utility). Also, if you have any accessories like an external thumb drive or USB hard drive, try disconnecting these as well, to rule out issues with them interfering.

We noted you wanted to try doing a clean install of macOS. While it's likely that things could be resolved without needing to start fresh, you can find the steps for that here, if you'd like to continue with that: Erase and reinstall macOS

Take care!

How to create a bootable installer for macOS - this needs to be performed from an Apple Computer compatible with Catalina. Once done - Shutdown computer and disconnect All External Drives except the newly created Bootable Installer. Restart and immediately Hold Option key. This will load the Boot Manager and choose the Bootable Installer.

Notation - this method will Remove ALL DATA from the Drive - can not recover them.

Follow the Steps # 5 to # 15 from Colleague @Jack-19