There's already some funky interoperability that comes from the underlying structure of communities kind of being user accounts, where mastodon users can follow Lemmy communities, and post to communities by mentioning them. But it's not pretty.

If you put the mention at the top like Mastodon defaults it'll look very messy on Lemmy because it will be trying to insert a MD link in the title field. If the mansion and hashtags are placed at the bottom of the post instead though, the post will appear fine on Lemmy.

There are a few guides on how to create posts that are compliant, Basically it's like this:

[Title] separated by blank line [Body]

[Hashtags (optional)

[Community mention] *you can only mention one community and if you want the post to appear on Lemmy that Community should be the first mention. If you want to mention people on Mastodon their mentions must come after.

Biggest drawbacks currently are:

Title will be repeated in the body
Issues mentioning people in addition to the community, also can't post to multiple communities at once.