Reinstall Prompt But Not Reinstalling

I have no idea how this is happening. I have a stable NextCloud install that has been running for several years. I have done nothing recently, but all of a sudden it has stopped working and I get the error “It looks like you are trying to reinstall your Nextcloud. However the file CAN_INSTALL is missing from your config directory. Please create the file CAN_INSTALL in your config folder to continue.”

This is similar to Reinstall prompt but nor trying to reinstall and Reinstall error but not trying to reinstall, except there are no permission issues, config.php is in the right place and looks fine, and I have not done an upgrade for several weeks. The only thing I can think of is that the backup extension ran over the weekend… but I have no idea how that could have contributed. Also, I can’t figure out how to restore that backup without running the reinstall and thus jeopardizing my data.

I am just going to do a DigitalOcean droplet restore, but I have no idea how this happened.

Does anyone have any insights?