Error message 5101f

What format is the drive? Earlier Macs may require MacIS Extended Journaled instead of APFS

Error 5101...

So, according to the articles, I have an incompatible Boot ROM version (or commonly known as BIOS). (To check it, go to the Apple logo - About My Mac- System Report - Hardware and see the number of Boot ROM version)

And that was right! I have two other MBPs and the Boot ROM versions were 428 for the 2014 and 424 for the 2015. The problem one was still at 192. My speculation is macOS has something similar to a compatibility mode so it could run on older BIOS versions but couldn’t boot from the Recovery Partition, especially Big Sur. I bought this Mac with no SSD and put in an SSD with Catalina pre installed, so the BIOS was probably not updated.

So how I solved this was pretty time consuming, but it worked! I used Shift Cmd Opt R to get Yosemite back on the SSD. Then I went to App Store and updated to Big Sur. After a longer than usual update and many more restarts that took about 3 hours total, my Boot ROM version was updated to 424 and the problem was solved.

EDIT: I got another one with ver. 180 firmware and when I trigger IR it doesn’t error out anymore, but the latest OS it could go up by IR is Catalina. From there I could manually update to Big Sur 11.1 but the firmware version stays the same. And of course, no access to Recovery partition. They fixed it in a half-assed way.

https://www.reddit.com/r/macbookrepair/comments/kab0an/error_5101f_on_macbook_pro_2015_and_how_i_solved/

OK, that is good, that is the drive you want o install to...

1. Start up from macOS Recovery

To start up from macOS Recovery, turn on your Mac and immediately press and hold one of the following combinations on your keyboard. Command-R is generally recommended, especially if you never installed macOS Sierra 10.12.4 or later… https://support.apple.com/en-us/HT204904#notupdated

Command (⌘)-R

Install the latest macOS that was installed on your Mac.

Option-⌘-R

Upgrade to the latest macOS compatible with your Mac.

Shift-Option-⌘-R

Install the macOS that came with your Mac, or the closest version still available.

2. Decide whether to erase (format) your disk

If you need to erase your disk before installing macOS, select Disk Utility from the Utilities window, then click Continue. You probably don't need to erase, unless you're selling or giving away your Mac or have an issue that requires you to erase. Learn more about when and how to erase.

3. Install macOS

After starting up from macOS Recovery, follow these steps to install macOS:

1. Choose Reinstall macOS (or Reinstall OS X) from the Utilities window.
2. Click Continue, then follow the onscreen instructions to choose your disk and begin installation.
3. If the installer asks to unlock your disk, enter the password you use to log in to your Mac. If it doesn't see your disk, or it says that it can't install on your computer or volume, you might need to erase your disk. 

1. Please allow installation to complete without putting your Mac to sleep or closing its lid. During installation, your Mac might restart and show a progress bar several times, and the screen might be empty for minutes at a time.

If your Mac restarts to a setup assistant, but you're selling or giving it away, press Command-Q to quit the assistant without completing setup. Then click Shut Down. When the new owner starts up the Mac, they can use their own information to complete setup.

If you never installed macOS Sierra 10.12.4

If macOS Sierra 10.12.4 or later was never installed on your Mac, macOS Recovery works differently:

• Command-R is still the recommended way to start up from macOS Recovery. This combination makes sure that the installation isn't associated with your Apple ID, which is important if you're selling or giving away your Mac.
• Option-Command-R installs the macOS that came with your Mac, or the closest version still available.
• Shift-Option-Command-R isn't available.

https://support.apple.com/en-us/HT204904 

Once in Disk Utility choose theView menu & Shaw all devices, what format is the top left one say?

Sorry, didn't re-read everything! :O

In your pick, highlight the U, which is likely Macintosh HD renamed, what size & format is U ?

Mac extended journaled should be fine, but be sure in Disk Utility's View Menu item to select Show All devices, the highlight the top one on the left.

Are you starting up with Shift Cmd Opt R keys held down?

What Format did you erase to?

At top left highlight the Apple SSD SMD128 G thing.