Some websites block lemmy.ml links, for example Facebook as you can see in the screenshot below.
I dont know if this is because of the .ml domain (which is free and might be used by spammers), or because they are scared of Lemmy. Anyway, this doesnt mean that it is impossible to share content from lemmy.ml on Facebook or other sites, thanks to federation there is a relatively easy workaround:
There are a few caveats though: In the case of a post, comments and votes will be missing. You can fetch comments in the same way through the search. The other instance will also not receive any new posts/comments/votes made in the community, unless a user from the remote instance is following the lemmy.ml community.
The easiest way to avoid these problems is for you to make an account on the other instance and follow the community from it. Then every post/comment/vote will be delivered to the other instance, and the community should look identical on both instances.