Help me. This is my final college assignment, and it can't be opened "failed open to document"

Here is the same explanation by Colin back in 2019 after they moved some things around.

and here the official help page

https://help.sketchup.com/en/sketchup/setting-software-and-file-preferences

so yes, here we’re not talking about a crash, we’re talking about file corruption, auto save won’t help, only skb. until it can’t.

Whatever you do, people, don’t forget to manually save your work from time to time.