I would like to try playing Katamari Damacy but do not have Nintendo. Is there a demo version, even a short one, that runs on Windows 10? I checked the official site but did not find any Windows demo.
No there ist no demo of Katamari Damacy available for the PC, only for the Nintendo Switch. To test the game on PC, you could buy it on Steam and return it within the refund time period, if you don't like it.