I use discord to chat and play with friends, many servers have an nsfw channel to share things that you probably don't want to suddenly be on your phone screen in public. It will also filter images in dms.
It's not the end of the world, but it's ineffective at tackling the actual problem, if anything adds appeal by making content "forbidden". I'm certainly cancelling my cheap nitro I've had for a while because I'm not giving any company arbitrarily implementing identity verification any of my money.
I'll also probably look into setting up my own matrix server later...
I disagree that this will help at all. Certainly not to a degree that justifies restricting other people's freedom. Grooming happens in small circles and doesn't become substantially harder if teenagers can't access nsfw channels. Predators don't seek out adult-dominated spaces. Kids might be exposed to slightly less porn or something but they will still go to pornhub, and now an access channel where there are at least likely normal adults around that could give context id needed is restricted. Worst case they'll be driven to fringe spaces filled with predators.
And also, people don't just use nsfw channels for porn or questionable memes. People mark servers as 18+ for a variety of reasons, some have political discussion channels marked as nsfw to make them easier to avoid, etc.