@srasmus@fedia.io additionally to what BentiGorlich said, there's also different compatibilities depending on the type of post you send out.
Threads are received normally on Lemmy, PieFed and Friendica. If you added tags to them, they don't appear on Lemmy but do on the other two.
Threads received by microblog platforms, I am only familiar with two cases, Mastodon and Misskey. On Mastodon, they are received the same as Lemmy posts, title, link to the original post and if included in the OP, the embedded image. On Misskey, they appear as long microblog posts. And in both cases, included tags are displayed.
Microblogs get a bit wilder.
Hashtags must be included in the post body, instead of having a field for that.
If you send them to a community, or mention the community as an user, they appear in that given community. Some times they don't on Lemmy instances though so you may need to manually search using their links on an external instance while logged in there, and the post appears only in the instances you search it on from my experience.
Also on Lemmy specifically, the first paragraph is used as the title, so avoiding links and hashtags in that paragraph may be recommended.
On Mastodon, Misskey, Friendica and PieFed, they get received as long microblogs. Also though boosts are available for all posts and comments, if you boost, it only gets received by boost-compatible platforms.
Unlike threads, there's no dislike button in microblogs (though on Lemmy and Friendica at least that's still possible).
If you follow @bsky.brid.gy@bsky.brid.gy, your microblog posts also get bridged to Bluesky and other AT Protocol platforms. But threads aren't federated. Also do mind bridged posts only display the first 300 characters before linking to the original post, meaning if posting to Bluesky and Lemmy at the same time from an Mbin instance, hashtags and the headline must fit within those.