macbook pro 2015 upgrade to big sur frozen won

Thanks again for trying to help. I’m not entirely sure what you mean by a deep press. I have pressed and held the power button firmly for up to a minute, also 15 seconds, 20, 30, etc. with no luck. I have tried all key combinations, including the ctrl-option-shift with power button mentioned in the article you linked. No luck. A day later the installation is stuck in the same spot. The only way to restart has been to let the battery drain. Fortunately it did start again and then resumed the install, but hasn’t made any progress in 14 hours since I did that. It seemed to go a little further along the progress bar than when it was frozen before, but then it stopped and hasn’t advanced since.

Thanks again. I believe I've used a deep press, then. At least I’ve pressed as firmly as seems possible and for at least 10 seconds. I’m convinced my power button was damaged by the shop that replaced my battery awhile ago. The only way I’ve been able to shut down is by letting the battery drain. I did get it to restart this way and restarted with the shift key down. This got me to Set Up Assistant. But now that has frozen after I tried to cancel migration assistant. Waiting for it to power down so I can start again. It is stuck on Are You Sure You Want to Quit Migration Assistant? I may try recovery instead of safe mode. I do have a backup if I can get things back up and running.

Thanks for all of your help. I’ve been unable to install the upgrade or restore from my backup. Seems to be the end of this MacBook with too many issues — power key issue, a new battery needed (again), can’t upgrade and can’t get back to my backed up state. I’ve attempted all options in recovery mode, but am told there’s a disk error buy desk utility can’t find a problem when I run disk first aid. Restoring from backup ended in an error.

Thanks again for this suggestion. I’ve thought about that option and may try it to get a little more life out of this machine. The thing is, the Restore from Time Machine option in Recovery Mode was supposed to erase the disk, but didn’t seem to. I see Macintosh HD that thinks it’s nearly empty: 129.91 GB of 1 TB used and 870.22 GB used by other volumes. Then there's Macintosh HD Data that has 867.49 used and 132.64 other volumes. They both show 212.4 MB free. The disk image Mac OS Base system is 1.67 GB with 92.6 MB other volumes and 119.1 MB free.

Maybe Disk Utility can erase what Restore from Time Machine can’t. Before I do that, I want to try to get some files from my backup onto my work computer, and make sure it is functional, since the restore wasn’t successful. I’m hoping it’s okay because if my main drive and my backup are both shot, than I’ll be in bad shape. I have archived files and a lot is on DropBox or iCloud, but some files could be lost for good. That's why I don’t want to tie up my backup drive until I know what's there, and I don’t want to erase the MacBook drive (again) if it might be my only hope for recovering files. I haven’t given up on the Time Machine backup, but I thought I should be cautious and that there are enough ongoing issues that it’s time to replace it. Getting my old MacBook back for temporary use would be a huge help until the new machine is here and set up, and it would make it easier to take in for recycling or repair. But it also isn’t my top priority to be honest. I’ve had to find other ways to do my work and can only focus on repair when I can spare the old computer and Time Machine drive for many hours. 

Looks like the disk is fried. I did erase and install Mac OS Big Sur. This brought me to an old Mac Utilities window (when I came back to it). There my only option was to install Mac OS Sierra (not even High Sierra, so it must be my original OS from 2015). Tried that and it failed. There are now two new drives in Disk Utility Apple SSD Media SM1024G Media and AppleAPFS Media. I can erase ApPleAPFSMedia, but get an error on Apple SSD 1024G Media. It won’t even erase and says “couldn’t open device.” Both these drives appear to be full at 1TB or close.

The good news is that I have my data, and a new laptop on the way. I rescued the files I need so I can work until it arrives. Inconvenient, but not impossible to live with.

I know, but doing that or doing any key combination with the power key has no effect whatsoever.

I did unplug and let the battery drain till it shut off. When I plugged back in and pressed power, it came on and resumed the startup sequence, so I'll see if it is able to complete the upgrade now.