Hi @GeorgeFlorian ,
Here are the libraries you are looking for:
mavlink.io
A really nice project using MAVlink with the Arduino IDE is done by @Eric_Stockenstrom on his great
mavlink-to-frsky-s-port-passthru-converter
This is a very well documented code with lots of debug options.
It helped me a lot to understand the MAVlink communication.
Good luck!!