[johneth]

I think "over-18" posts on X within the feed are hidden behind a "please verify your age" button if you've not verified your age (in UK and parts of EU, probably Australia too). They're intermixed with non-hidden posts.

X lets post authors mark their content as NSFW, and I'd assume they're doing some sort of algorithmic checking or making use of user reports of content to classify content too, to varying degrees of success. It's definitely subject to the whims of the platform owner, given the sheer amount of racism, sexism, and porn that isn't marked.

My account is >18 years old so it never showed up for me (it just used the account age to determine I'm old enough), so I'm going by what others have said.

[inigyou]

That's pretty stupid, that means X has to verify your age. If the browser could just send a header saying whether adult content was allowed, the server could just respect that and not verify anyone's age.