MacBook Air Death Loop after Attempted Update

I have a 2020 MacBook Air that was on an early version of Catalina before I attempted to update the OS last week. I chose only to update to the latest version of Catalina, rather than a major update to Big Sur or later.

The computer went through the motions of updating, but took forever, attempted to reboot a few times, but never succeeded. Now when I boot up, I'll get to the login screen with my picture displayed and attempt to log in, but the loading bar will get about halfway complete before the computer restarts and shows a black screen with the Apple logo and a loading bar like it's attempting to update. It will make some progress before shutting off, and the loop restarts.

The Genius Bar looked at the computer but wasn't able to mount the drive. (The technician said that the computer did detect the drive, but it appeared in APFS, which he said it shouldn't have been, and also showed 0 KB free data, which is incorrect.) A third party support company was able to get the drive to show the correct amount of storage and free space remaining, but also wasn't able to mount the drive.

Is there anything else I could do here beyond getting a third-party servicer to attempt data recovery ($450+) and then reinstalling MacOS from scratch? I have backups of my most important files but not everything.

As an aside, I'm truly shocked that an official MacOS update is so buggy that it risks irreparable data loss and that Apple doesn't have a big flashing alert telling you to do a full backup prior to an update. Apple has the luxury of designing all the hardware its systems run and generally makes such seamlessly high-quality products, so I'm baffled how it can't provide a less risky update method or at least adequately warn of the dangers.