[2023] Which DLCs to activate/deactivate for showing this game to a new player ?

I'll give the minority opinion on this one.

Run all DLC, but tell the new player to just use presets in the designers. And don't worry about MIOs. Just right click that notifier until they are ready to play around with it.  

Ruck said: Victoria I and I totally forgot how alien and strange some concepts are for beginners which never played those games.

Yep.

You've been around long enough to remember when there wasn't a name for the genre of Paradox games. And I think you've even been around long enough to remember that EU1 was just a conversion of a tabletop game and how those tabletop rules were subject to abuse on computer. (Farming minors for 200 ducats at the end of every truce period as an example even if their income was 1 ducat a year.)