KDE is not a Mint supported DE and the KDE files are not in the Mint repos.
This can be made to work if you're experienced but is definitely not a good idea for beginners. It will eventually break, and dependency hell is a thing.
For a KDE option suitable fir beginners, Fedora offers KDE as does Ubuntu, or there's KDE Neon
OK, in broad terms you want a distro that is reasonably up to date, but doesn't have to be bleeding edge.
I run Mint Cinnamon and Arch KDE for the limited gaming I do, they both work perfectly fine.
Almost all games that have a Linux port will have the support & requirements specified for Ubuntu, which has a KDE flavour, however most people won't recommend Ubuntu (for good reasons). An Ubuntu derivative with the issues removed however is a decent choice: Mint or PopOS.
Mint is by a long way the most recommended Linux distro for beginners and for good reason - the install process is easy, the community is supportive, and it does pretty much everything straight out of the box.
Cinnamon desktop environment is customisable, not as much as KDE. If you're really keen on sticking with KDE then either EndeavourOS (which is basically a bundling of Arch so it's easy to install) or KDE Plasma - which is Debian based but more up to date than Sid I believe.
I don't recommend Arch for beginners unless you're highly technical and willing to RTFM.
Most windows games will work in linux via proton/wine etc. ~You're~ Your only really blocked ones are the couple of companies that insist on kernel anti-cheat and are anti-Linux (EA I think ?) it's a handful of AAA games that are locked out.
Generally you don't need any hardware changes nowadays, in fact it's often the other way around - stuff that W10 & 11 no longer support can often be made to work on linux. AMD & Intel GPUs are less troublesome than Nvidia, but it's generally not a big deal anymore.
Reddit's /r/linuxgaming has fairly reasonable people (for reddit) and a fairly deep archive that will allow you to search for the specific games you most play, and ways to get them running.