Not a single social media platform have this warning.
We tend to believe we are being hacked when our passwords got stolen, in reality, unwanted graphic content has much more power to manipulate someone in internet.
Looks like even FireFox phased out BLINK around 2013. And it is claimed that it never was a standard tag.
Mastodon has a free-form content warning field you can use for any post.
The flashing lights warnings definitely appear (these days) when many games start too.