If Safe Mode is showing this, you’re left to try Diagnostics (a few of the oldest Macs compatible with Catalina will need Hardware Test) and Recovery, but it’s possible that your Mac has a storage corruption, or is having hardware problems.
The I/O activity of an update or upgrade can push a failing hard disk further into failure, for instance.
Add-on cleaners and add-on anti-malware apps and other similar add-on apps can cause corruptions, too. And sometimes a crash or a hard shutdown can cause a corruption.
Run diagnostics (or hardware test), and see if there are errors.
Then see if Recovery can restore this.
If you don’t have a current backup, use Recovery to get a copy of your storage to available (blank) external storage device. If you can.
If you do not have a current backup, get a backup first, and get a backup before any other tests or operations.