I expect this topic has been well explored but I don’t know how to search for it.
recent documents lists the files. But each is marked does not exist. Following an online hint, I search from home with *.odt and find 4 of the less important of 20 odd files. *.ods gets 5 more but nothing updated since March 25
Do you have an online synchronisation program, e.g. OneDrive? Sometimes they make files available only online.