Is TikTok how the practice of censoring one's own swears came about? I've seen it on a lot of social posts and have been wondering. Besides it being hokey (why use the word to then immediately self-censor), it also instantly dates the poster as someone too new to the world to be able to make an interesting post. That last part is just an opinion, though.

This is more of my personal axe to grind, but it's important to view this as a result of monetized content and highly algorithmic feeds. It is my understanding that these platforms don't even really remove this language, just demote it, but that the culture on these networks is entwined with people who post for money, so anything that reduces exposure or payout is shunned. This is true for TikTok, Instagram, YouTube (shorts).

That said I wouldn't even assume "s3xual" is a result of this. It smells of older censorship to me, all the new stuff is video-first, so phonetic substitutes are more characteristic.