Here's an complaint thread (not mine) with a screenshot: https://old.reddit.com/r/hoi4/comments/suurzs/paradox_this_is_unacceptable_in_a_paid_product/

I personally get more annoyed by in game presentation of features and then getting hit with a "you need to pay extra to use this", that's basically an ad as well and it's constantly there in the main gameplay loop. Bye bye immersion. It's an annoyance every time that you are confronted with it, which in most paradox games is basically all the time. It's like buying a car and then having to pay extra to unlock the seat heating that is already installed.

I could probably work around it by not auto updating paradox games and installing mods to remove some of the ads, but for 1 campaign every 2 years that's just not worth the hassle for me. So I simply don't play paradox games anymore.