Code -5101F

My notes on it...

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/

There is no Active and Functioning Internet Connection

Suggest using an Ethernet Cable from Computer to Router