[2023] Launcher won't recognize saves

Local save files are in Documents/Paradox Interactive/CK3/save games/ folder; your save files are physically present there, are you saying? If so the only known reason why the game would not show them is if they are so corrupted the game cannot recognise them as valid save files; how that could happen to multiple saves at once I have no idea.

Also there is Documents/Paradox Interactive/CK3/last_save.ck3 , if you copy that to the /save games/ folder does that load?  

In general, any corrupted computer file is probably irrecoverable. But it is not impossible the corruption is relatively minor and can be edited out. The good folks in the User Mods forum here are probably your best hope for that.

However it's a huge worry that it happened to them all at once, I struggle to come up with any explanation for that! Normally only a save for the campaign that is currently open could be corrupted by, say, a game bug or a computer glitch. Save game files not currently open ought to be unaffected by anything like that.

It is probably worth making a thread in Bug Reports and attaching ALL the affected save game files there, with an explanation of the circumstances.

Sorry this happened to you, whatever the cause!