Please don't run scripts that a random person uploaded to Github if you don't know what you're doing. I didn't see anything malicious here, but most of the stuff is useless and some of it is even detrimental (e.g. the LLM "thought" the outdated Ubuntu Nvidia ppa was a good idea).

If you want to game on Debian, you can do that just fine. Installing Steam and Nvidia drivers (if applicable) should be sufficient for most people. IMO, the main issue with gaming on Debian are the very old GPU drivers (Nvidia 550, Mesa 25.0). This can be fine on older hardware, but is the reason why I wouldn't recommend Debian for gaming in general. The script you linked doesn't help with this at all.

If you really want these "gaming optimizations", for the limited benefits they provide, I would recommend that you just use one of the distros that ships them. CachyOS, Bazzite, Nobara, Pop OS, or PikaOS all seem like a better choice than these scripts. At the very least the maintainers of those distros will integrate everything and perform some level of QA for you.