YouTube, Discord, Spotify, and X are some of the ones I know of.
What's strange is that YouTube in particular is age-gating in the U.S early because of the Online Safety Act. I imagine every platform is going to follow suit out of fear of liability.
Discussion
Oh, I only use one of those (YouTube), and I honestly wouldn't need to use it much longer if I had to give it up.
I had only heard about it with Reddit, in the UK.