We’ve been using COSMIC on our systems since summer of last year. Some graphics drivers have issues, particularly NVIDIA drivers using Vulkan on Wayland. There are some XWayland bugs from time to time. It is very usable as is, but some settings aren’t implemented yet, and some toolkit features aren’t fully implemented.
NVIDIA believes they’ll have the Vulkan on Wayland issue fixed in the 550 driver that they are planning to release early this year. Someone’s working on a fix in wgpu that happens to also boost performance for every driver in demos.