KDE plasma has this feature. You can choose between forcing x11 apps to scale or allowing x11 apps to scale themselves. Some apps won’t scale at all when you do the latter option but most at least increase the font size or have their own way of scaling.

Firefox has librewolf for desktop.

I mean it’s not surprising if theyre not actively trying to troubleshoot their problems. I run Linux on both my desktop and laptop and I never had a perfect experience with either. On my laptop a few years ago I tried installing Ubuntu but my trackpad sensitivity on linux was way too high with no easy way to change it. I also needed fractional scaling and at the time Ubuntu used X11, I found some command on the Ubuntu forums to enable scaling in the settings and it gave me screen tearing. After a few hours of playing around with different commands I gave up and weny back to Windows.

On my desktop I use Nvidia and have two monitors with different refresh rates. That causes a lot of issues and I just have to put up with it.

Edit: I use Arch on both of them now and have found solutions to my problems but especially my laptop issues were very annoying.