As far as I know, the protocol is pretty much standardised and it’s now up to the desktop environments to support and implement it, and that transition took a lot of time. GNOME has already been there and on its way to winding down X11 support, KDE has also been building up its Wayland support too. Waydroid (Android container software) requires it, and Valve uses it for Gamescope on SteamOS too iirc, to give games a more predictable place to render themselves on. Everyone’s got a kick up the ass with regards to Wayland support recently, but for smaller, independent/non-corp backed or niche software, of course, it’s gonna take a bit longer.
I’ve tried Euro Truck Sim 2 with my G29, which was built for PlayStation but can work on PC with drivers on both Windows and Linux. On Linux, PS4 mode doesn’t work on Linux, but PS3 mode does - the main thing is you lose the speed indicators on your wheel, if you really want them speed lights you’ll have to go Windows and install G HUB.
Some say PS3 mode disables clutch support since that was the case when using it on a PS3 but IDK if this is the case on PC and specifically Linux. Cursory search points towards no.