Like 10-15 years ago I was into linux and tried a bunch of different distros (PCLinuxOS, Mint, CentOS, OpenSuse...) and was quite happy with the, then, limited options of gaming on linux (It was the time Valve released TF2 for linux)
But time passed, I got a new PC and didn't bothered install any linux distro (because I got a small HDD and didn't wanted to split it in partitions for linux)
Back then stuff like Proton did not even exists, so today I'm kind of lost and don't know what flavour I should pick, so here I am asking for advice
A couple of relevant details about the hardware, my PC is a little bit old (i7-7700) I hope that's not an obstacle to enjoy gaming on linux I also have an Nvidia graphic card
Also, while most people just use Steam I also use GOG regularly, if that matters
I've been using Linux - off and mostly on - since a year after Linus released his kernel, and so have tried a bunch of flavours. I agree with aperson: you'll receive lots of recommendations, but only you know what you like.
My daily driver is Ubuntu on an i5-7200U (Lenovo ThinkPad), and before that it was Kubuntu. My main PC is an i7-7900K, so similarly long in the tooth as yours, and both CPUs run the Ubuntu flavours just fine.
My personal preference is currently Kubuntu (faster, lighter, and fewer "this is how it is, and you'll be glad for it" decisions). But there are so many others to try. Find a bunch that support Proton and gaming, grab their "live CD" versions, and see which ones work for you.