Like the other comment mentioned I'd try https://www.cgsecurity.org/wiki/PhotoRec first.
Just a heads up with proper data recovery it's usually a good idea to dump an image of the media card to your drive and do any data recovery attempts against that image, not the media card itself. I would usually use ddrescue for that but you'll probably be okay with standard dd too if the card itself is fine (as you said the deleted files were user error, not a failing card).
PS - You should definitely not use the media card in the camera until you're done with recovery attempts, the more you use it the less likely you'll recover anything off it.
On Debian the older Nvidia GPU would still work fine with the default Nouveau driver (open source non-Nvidia), I think(?) it'd be the same on Kubuntu/Ubuntu. Since it was an upgrade maybe you just need to re-enable Nouveau on your system? It's not something I've ever done but doing a quick online search came up with some instructions here https://gist.github.com/vredchenko/42381e9cff3f1e162cb47cfd6479c459 , it looks more or less correct I'd just double-check before rebooting that Nouveau is not being blacklisted in /etc/modprobe.d
You could try that & see how it goes before doing anything more drastic. You're not going to do any heavy gaming with Nouveau but it should handle day-to-day tasks fine.