@imc67 Looks like you have to refresh the UI. I wasn't able to 'save' the configuration in any case because of the other bug you already reported.
So, I had to edit /app/data/production.yaml manually to be:
theme:
default: 'dark'
And then I restarted the app. I then got the theme:
[image: 1593124163810-400f5bc0-49f6-4162-bb36-fdc8839f688c-image-resized.png]
