In practice, because Rust libraries are always statically-linked, the MPL-2.0 is equivalent to the LGPL in spirit. Meanwhile, because of the static linking restrictions in the LGPL, the LGPL is effectively no different from the GPL. Hence, you’re going to find a lot of open source copyleft projects from the Rust ecosystem preferring either GPL or MPL-2.0, where MPL-2.0 is used in libraries where LGPL would have used previously in C projects. Dynamic linking is essentially going the way of the Dodo.
Wayland compositors use IPC over a UNIX socket to communicate with Wayland clients. To increase security and enable sandboxed applet support, COSMIC applets use the security-context protocol for their IPC connection to the compositor. To be an applet, COSMIC applications use the layer-shell protocol to behave as an applet. Neither of which were made for COSMIC. Some other Wayland compositors support these protocols. You can see which compositors support the protocols at the bottom of the wayland.app protocol pages.