If you’re using dark mode, then logically you get thumbnails based on the current appearance.
However, if you disable the General > Appearance > Use dark background for documents, the thumbnail is still created as dark mode. @cgrunenberg, is that expected?
I have tried that option before posting here @BLUEFROG , and can confirm the statement from Christian. This setting has no effect on this.
I do use that setting thou for the background of the documents. Yet I wonder how to make sure that those documents are actually well visible in the overview (similar to PDFs). I feel the setting “dark background” should have NO negative effect on how those documents are presented in the UI overview - maybe they should get some slight edge - to make them distinct.
Just look at this example: do you even see that there are two documents here?
Those are markdown files with text (and sometimes images i.e. markdown links to image files). The fact that there is an image has 0 impact on the thumbnail in my experience.