If you are not fan of extensions, then check this blog post on how you can add dark theme to your own Mendix app:
https://www.notion.so/gajduk/How-to-add-a-dark-theme-to-your-Mendix-app-in-5-minutes-27ea7559165b46e3a3aac2f19cef8836
Andrej,
Did you also notice that the new topbar in Sprintr (normally says Developer Portal and has search bar and profile image) disappears when using DarkReader (since a couple of days). Or is it just for me?
When disabling DarkReader it re-appears.