https://abevoelker.github.io/how-long-since-google-said-a-go...
Of course there are alternatives now, but I like to plug this page whenever I can.
The workaround was to back everything up to the "Google Drive" folder since this seems to be the only folder that Backup and Sync can actually restore.
At one point I set it up to use my second SSD as the local storage. Then I needed that SSD elsewhere, so I just took it out. It was impossible to restart the damn thing. It kept complaining about missing folders. I even tried uninstalling and reinstalling it, but it kept its settings.
Since I barely used that machine, if ever, and I'm not particularly familiar with Windows, I never really looked into how to completely clean up the configuration. But the point is that there clearly are some pretty stupid decisions about some products.
System-wide settings and state should be stored in C:\ProgramData.
But on a more useful note how I have handled this in the past is to download the complete Google Drive data using Google Takeout. Not the greatest solution but it has worked.