I would agree pretty much with you, but OP posted this 13 hours ago. In ten hours only one person replied and only had a similiar issue about one of the points.

Kubuntu is no a popular distro of choice within the gaming space so i doubt it will easy to find someone who can help to troubleshoot their problem. Also i think i read somewhere that Ubuntu had some problems with 32 bit libraries. I may be wrong tho.

As i replied on another comment, changing distro will probably be the fastest way to solve or at least diagnostic the problem. It’s probably extreme but better than nothing. I would also try the flatpak version first.

As other replies told you, trying another distro to check will probably be the fastest way to solve the problem. I don’t think many people have experience with Kubuntu.

If you don’t want to change distros, you could try the flatpak version, it has their own package of drivers, and runs in a different runtime.

Just know that the flatpak of steam is not official but a community project. I had used it before without problems but i like to be clear about it.

Thanks for sharing, i haven’t been able to find a good guide, will check it out. Or more accurately a guide that i can follow with ease.