Project content gone on Win 11

I’ve just gotten a new PC and installed the older version of Scrivener (that I’ve been using on both PCs since I don’t have a license for 3), and opened the project that I have been saving on an external hard drive. When I open it on my new PC, some content will be missing - as if it’s from a state of months ago.
I’ve attached my old computer, and when I open it there, everything is back. How can that be?! I’m at an utter loss. Strangely, when I saved the project on a different name, that folder won’t even show up on the Windows 11 PC.
I’m so confused and don’t know how to fix it. Anyone have any ideas?

is confusing agree. When use old external drive, look in options and backup to see where saving new backups and adjust to your preference (or use dropbox if multiple computers) and adjust your number of saves and make sure save on exit is checked and close project then will have saved on windows 11 and can reopen to check if works (should). Do this for all the old projects and should take of issue. Have windows 11 without issues, but use Scrivener 3 which I love, lots of nice new features. Good luck.