Hi,
There is a new version of the PLantUML plugin of QownNotes (
https://www.qownnotes.org/). This new version renders diagrams in the background and is very easy to use. It can be found in the plugin repository of QownNotes, or here:
https://github.com/qownnotes/scripts/tree/master/render-plantuml
It should work on Linux, Mac, Windows, it works offline. And maybe, it should be included in
https://plantuml.com/fr/running