The problem is that such a line doesn’t exist, because they’re always looking for ways to increase profit for shareholders. On day X, they’ll be fine offering you an ad free sub, but on day X+Y there will be a meeting where they discuss what they can do to improve their revenue numbers and someone will suggest adding just a few ads to the ad-free tier.

This is why people go scorched earth with adblockers. There’s a lot of discussion about “good” ad networks being allowlisted, but they are all just one missed earnings report away from implementing dark patterns. None of them are trustworthy.