I've switched to KDE neon (again) and I think I've decided I like it better than Kubuntu at this stage, because it comes packaged with newer stuff from KDE than Kubuntu, and there's less software bloat of things I don't want/need installed on a fresh Linux distro installation. Also, GM games run out of the box on KDE neon, without needing to install any packages from the terminal, because it's based on the same LTS version of Ubuntu currently supported by GMS2. It only gets LTS release updates, iirc, so that's a plus in my book. I prefer having a Linux OS that is as stable as it can be, and KDE neon is pretty solid.
And for all the Canonical and Microsoft haters out there, KDE neon, just like Linux Mint, is completely detached from direct association with and influence from Canonical and Microsoft, despite both KDE neon and Linux Mint being based on Ubuntu, they are in no way affiliated with these two companies you might be worried about. It's a win/win for GM users looking for a vanilla KDE experience, while having a Linux OS that will support your GM games as-is. Linux Mint dropped KDE support, so KDE neon could not be a better option for those of you who fit this particular audience. I'm still saving up to get the KDE Slimbook.
https://neon.kde.org/
These screenshots aren't much to look at, but I find there is beauty in its simplicity.
However, KDE neon is anything but lightweight, much like any other distro running the K Desktop Environment, and thus I would steer clear of trying to install it on older machines, especially if there is data on your older machine that can't be replaced and you don't care to back up. I've almost corrupted my Windows install on one of my older computers, just trying to install KDE neon as a dual boot with Windows 7 64-bit. KDE neon also has no 32-bit version, as it aims to have the latest KDE technology.
That said, if your machine is particularly old or slow, with terribly outdated specs, I'd recommend installing something a bit faster and more light-weight like XFCE as your desktop environment. Xubuntu has a very bland interface. I'd go with Manjaro XFCE personally, but because it is based on Arch Linux, it won't necessarily be guaranteed to run your GMS2 games out of the box without a visit from your Manjaro package manager. XFCE is pretty well known for being a desktop environment that can make the most out of your machine's hardware and specs, with the best performance, and very little resource usage. But if you want your GMS2 games to run then use Xubuntu.