I made a rough proof-of-concept that tries to fix tiktok embeds here.  The code is too long to post, so you can find it here:

https://git.vern.cc/gg/endchan-scripts

Example
 >>/jp/1507/
https://www.tiktok.com/@mina14504/video/7546151220046613776 [Embed]

It's really rough, but it does manage to successfully embed tiktok videos.