I know this is 2 years later, but since there weren’t any legitimate answers in here:

https://github.com/pablouser1/ProxiTok

And for those of you who just have friends that insist on sending tiktok links and you just want to quickly see the content you can use:

https://proxitok.pabloferreiro.es/

Someone correct me if I’m wrong, but once an instance has been defederated with another, you will not be able to see posts from users associated with that instance, even if they post into a community that you are federated with.

Relevant xkcd: https://xkcd.com/2169/