While Darkmode is not currently available, may I suggest changing your Trello background? While it doesn't give you exactly what you want, changing the background has helped me.
I know. It helps a little but not really a solution.
Currently i just use the web version + dark reader.
And i mapped a keyboard shortcut to launch the url using Keyboard Maestro.
I’m not in pain. My dramatic post was a bit of joke. Its a real request. But i can manage😁
1 year later, and still nothing. Changing the background helps with boards, but then your eyes suffer even more when you jump from a dark board to Home or Workspace view that is bright white.