Xfce
I’ve daily driven every major DE except KDE (GNOME, Xfce, MATE, Cinnamon) and I always ended up switching back to xfce. I’m not a fan of GNOME’s workflow and since it’s not that customizable without extensions, that made me switch from it very quickly. I used Cinnamon on Mint for a few months and while the experience was mostly fine, it sometimes felt a bit laggy. As for MATE, while I love the GNOME 2 layout and it’s a relatively lightweight DE, I encountered plenty of visual bugs there and I could very easily replicate that GNOME 2 layout on Xfce (without a system menu, but still).
All old valve games have long been deprecated on macOS since apple dropped support for 32 bit applications in 2019 and valve seems to have given up on mac gaming all together.