Many of us have. I enjoy KDE but COSMIC looks very slick and when listening to the developers it sounds like it’s really thought through. They have considered so many details. For selfish reasons I’m glad to see it’s already being worked on for openSuse.
Various projects. With C I wrote drivers and networking stacks for embedded systems, with C++ I worked for years on a the networking layers of a now long gone smartphone OS. With Rust I’ve been doing hobby projects like a library+application (win/linux/macos) for controlling WeMo switches on the LAN. Most recent is a Memory+CPU usage monitoring applet for the nascent COSMIC desktop environment.