Filebeat service wont start even after 'test output' and 'setup -e' shows positive results

One thing You are not referencing the correct docs.. you are looking at 7.17 (which you should use) but your say you are using 7.4 so you should use the correct docs

Also you can tail the journalctl with -f .. I think the interesting lines was before what you showed.

You could also set

logging.level: debug