The compositor has to support tearing too I believe (I’m not sure all of the main 3 do, and e.g. wlroots only very recently got most/all of the pieces and I’m not sure sway supports controlling it) and will probably be where the option is exposed. And this is specifically about XWayland, where the support is even more recent. So I wouldn’t necessarily expect it to work yet, but maybe Plasma is ahead of things here.