off the top of my head: ip kvms, keyboards, 3d printers, home assistant, cameras, zwave or zigbee. Their moat is superb software support and established ecosystem. I think their most challenging competition would be ESP32s or mini pcs. Source: my ahh
Have you tried? There are some really nice DEs out there. KDE has been killing it lately, and there are so many good tiling WMs too. It all depends on what you're looking for from a desktop OS though, so without elaboration I don't know if you're missing out or there's that one thing that's lacking in the Linux desktop world right now.
Not unless you have a HiDPI display and rely on some non-Wayland-native apps. Causes blurry apps which can be headache inducing. It is a known issue being worked on though.