Yea posting from mastodon to lemmy is a nice way to join the two platforms actually.
I keep encouraging mastodon users to do it more, as they don’t have any groups and hashtags and not great IMO.
For those interested, I’ve written a little demo of doing so from mastodon, with comments/replies that provide links to the resulting lemmy post: hachyderm.io/@maegul/110483509521476095. If you think it’s helpful, feel free to share it around to anyone else you know that might be interested in posting to lemmy from mastodon.