Adapta theme and cinnamon alt-tab thumbnails
I have reported an issue regarding too small thumbnails in the alt-tab switcher to the cinnamon tracker and they said the problem is in the theme:
https://github.com/linuxmint/Cinnamon/issues/7739
Here are some further comments in manjaro's forum:
https://forum.manjaro.org/t/manjaro-theme-not-playing-well-with-cinnamon-alt-tab-switcher/52301