I addressed how this affects fingerprinting in this comment.

The short answer would be no. Tor browser uses dark mode by default, and since this theme is also a dark (mode) theme that doesn’t change.

The longer answer is if you have JavaScript enabled it might (in theory, but I don’t know how practical this is) be possible to use some kind of exploit or side-channel attack to figure out what theme is enabled or which themes are installed.

So that is something you should keep in mind for your threat model.

My answer is based on personal experience, some basic googling and asking the Tor community. But it still can’t hurt to do some additional research yourself. 😄

Feel free to correct me if I’m wrong.