I'm using the amdgpu driver with Window Maker, i didn't need to do anything special for it to work. FWIW variable refresh rate also works (my monitor has VRR support and displays the current refresh rate in an overlay), though it needs an option in xorg.conf to enable.

Note that i do have tearing in the desktop if i -e.g.- move windows around, but this is something i want as i do not like the slight input lag compositors add (even on my 165Hz monitor). However there isn't any tearing in VLC or in games (which, depending on the game, i might also run with VRR).

AFAIK the modesetting driver got VRR support only recently and the TearFree mode only just a few months ago so if you used that you might have used some older version.

Though if you tried a compositor, i don't remember using any compositor that didn't do some form of vsync to avoid tearing. I just started KDE Plasma with Xorg in another virtual terminal with its compositor and default settings (i started it as a different user with default settings that i sometimes use for testing) and there wasn't any tearing at all even on the desktop (again using the amdgpu driver).