If you do not see GPU Effects at the top of the Settings menu, it is disabled. There is a beta in the beta,edge, and candidate snap channels that is a very different build based on a much newer version of Qt built on the same Ubuntu version as all of the other components. Please try it. Alternatively, instead of switching the snap channel, you can test the portable tar or AppImage without messing with your “installation,” which you can get here:
Portable tar, AppImage, and Snap are all the same build with different launch wrappers.