They lost all their users that provided value for reddit as a platform. Reddit will surely continue to flourish as a way to show ads to children and astroturf Google search results for product reviews. But I've noticed a ginormous drop in posting quality since they neutered their API. Even small subreddits that were fairly active are now filled with spam and engagement farming, moderators aren't interested in cleaning anything up because their app to do so is trash, users don't want to post because the subreddit is shit up with garbage. It's gotten bad.

Any examples of such subreddits? For the ones I visit, like askhistorians, programming, etc, it's been business as usual.

That's because askhistorians only let's other historians ask questions. I've tried asking some serious questions there before and I always got immediately deleted. IIRC it was always something about how the quality of my question was beneath them.

That's definitely not true, most questions on there are from amateurs. If your questions keep getting deleted, there is something wrong with how you are asking your questions, perhaps they are too broad to be unanswerable.

Recent example I've noticed, /r/patientgamers has had repeated posts in my feed that are the exact same copy of "no matter how many times I try, I just can't get into <GAME NAME>"

I didn't used to see these copy pasted posts regularly at the top of subreddits but it happens frequently now.

Well, that's to be expected from such a sub, who'd recommend games from recent history over those of, say, the Pong generation. That is simply how people grow up.