FYI, using the unmodified Dark Theme (OOTB) as our default theme has resulted in GSC complaining:
Page is not mobile friendly
If we change the default theme, for example, to Graceful, GSE will not complain and Google will report the page mobile friendly.
It’s strange that when we look at Google’s view (the screenshot) Google is reporting the desktop view as mobile.
Possible to get this fixed, since we much prefer the Dark Theme, as default: