Breaking News:
… which in part may be slightly embarrassing …
But I’ve been obtuse enough to look only for configuration elements of the productive machine that I thought must be missing on the laptop. Or for other additions like this thread about maia andmanjaro-gnome-vanilla which didn’t/doesn’t work for me (rather than ‘substractions’).
Now, 7 weeks after starting that search, I found a gtk.css in ~/.config/gtk-4.0 of the laptop, which doesn’t exist on the other machine. And that contained the specification which blocked the one in dconf from being applied to the corresponding Apps.
Since I don’t know if this unsolicited preset from the initial install would be re-introduced by a later update if the file isn’t found, I exchanged maia with blue - and that was it.
While this increases my theme’s calmness, which I really enjoy, there are still two drawbacks:
I didn’t find a corresponding entry for a preset of ‘attach-modal-dialogs’ (which currently means to avoid (not to install or to dump) those apps (eg. ‘Console’, ‘Texteditor’, … in favor of ‘Terminal’, ‘gedit’, …) wherever possible).
The putatively permanently resolved display issue re-appears occasionally - but to a minor, probably bearable degree.