Mods aren't fully banned but they can make the game harder, easier and can give a disadvantage so read this if you are someone with mods

ACCEPTED MODS:

• New Civilizations
• New Scenarios
• New Maps
• New Cities
• Graphic Changes

NOT RECOMMENDED MODS:

• New leaders (It can put you in trouble because the information can be changed, so if they are leaders for an already existent civilization try to deny them)
• Formable Civilizations (It can confuse you and you can accidentally be speedrunning a custom formable civilization)

BANNED MODS:

• Changes in current scenarios
• Changes in current leaders (With exception of the image but it can put you in some trouble)
• New connections and provinces in current maps
• New governments (Because even if you don't use it the AI can choose it changing the game for good or bad)
• New diseases
• Every change that can be done in the map editor (With exception of Formable Civilizations)
• Change the data from Terrain Types

That doesn't mean you can't use mods for AoC2, if you really want to play one edition with mods just create a copy of the game, in one you can put all the mods you want and in the other one just don't modifiy anything