Since I don't own one myself I have to rely on reports from other people to know that this and the previous Captain Disaster games are compatible with the Steam Deck. One of the test team for Riskara has kindly created a video showing the demo being played on it.
Apparently the Steam Deck did show a message saying that the game might not be playable, so I don't really know what that's about, but it then worked. I'm not sure if the warning message is in relation to certain redistributables possibly not being available.
Anyway enough waffle from me, see the video below! With thanks to Ramon.