the serial monitor mostly does not work (while it's working fine for my other Arduinos)
compiling sketches generate warnings that they may not work properly "on this architecture" (but they do).
Must frustratingly, there seem to be few info and examples available online about the MKR's and the problems I encountered.
I'm starting to wonder if I'm maybe the only one left still using this not so good Arduino?
For some reason the port toggles for every upload between COM 8 and COM10
Of course there was still all the stuff I never saw before with the AVR's such as: COM8 suddenly appearing twice in the IDE's Tools-Port Selection
For me personally there's no challenge in spending a lot of time figuring out how to get the basic functionality to work. Therefore, I have decided to take up your advice and go back to the AVR boards.