Thanks @Orphée, I will check the forums.
I have a friend who has an old VGA monitor which I should receive in a few days. I will try again then.
For now I'll revert to my functioning DSM 5 and rest, I've been trying to make this work for days, numerous USB sticks, loaders, formatting USB flash drives... 😣
EDIT
@billat29 - unfortunately no luck with v1.01 - Syno Assistant doesn't find anything (and router doesn't see the box).