On startup, in the Continue Your 2021 Tax Return window, the most recent returns may NOT be shown, even though all are in the same folder, and each was saved in sequence from successive TTax sessions.
I save each tax file with a version number suffix and increment it for snapshots over time (e.g., Tax01, Tax02, Tax03,...). However, TTax might NOT show the most recent one(s) in the startup window. This first happened 3+ years ago, and I grabbed the first one in the list, which was the highest version number shown, but quickly realized this was not where I had left off. Restarting TTax did not change things. So I went to the "Find a Tax File" link and sure enough, the newer versions were there in the folder. If I reopen one of those missing files, then save it again, TTax will now find it in the Startup window list (as the most recently saved).
Since this just now happened again, I decided to spend the time to post this FYI.
TurboTax will only find returns that it saved and that remain as TurboTax saved them. If the file was moved or renamed outside of TurboTax, then TurboTax will not find it. As you have discovered, if you open the return in TurboTax and save it again, TurboTax will then be able to find it.