Might be the base game to prevent cheating

The mod menu has always been locked. Maybe someone will create a mod to unlock it, but opening the mod manager (at least the first time, maybe it has a "don't remind me" box) always displays a message that:

A) Paradox Interactive allows mods at user risk (so if you break your ♥♥♥♥ by downloading a mod, that's a you problem, not a Hae/Abstraction/Paradox problem.)

B) Achievements are disabled when mods are enabled.

We know the OG game had workarounds, so just wait for Workshop to refill on this end.