I've previously posted a few examples:
Is there a way to keep Linux responsive when at ~100% CPU usage?
I also regularly have my window manager crash when inserting my laptop into my docking station. Happens maybe 20% of the time. Sometimes even when it works the display scaling makes things blurry until I reset the scaling from 150% back to 100% and back again, then it's fine. Add to this a few annoyances with UI, but these are more forgivable.
There's all kinds of these small problems that compound to just make for a much worse experience. It doesn't just work but it needs to if it really wants to provide a viable alternative to normal people.
Keep in mind, I am not a "normal person" - I am a professional software engineer and I still find all this stuff super annoying.