On the left, the 404 Media Ghost account (@feed @404media.co), as viewed from my GotoSocial account, via Phanpy. On the right, the same account, as viewed from a Mastodon account, also via Phanpy.
What’s interesting is that the GtS account displays the entire text of the article, while the Mastodon account only shows the preview and a link…
You can also follow the same account from PieFed, but currently there’s nothing that comes up.
Vanilla Mastodon will totally display long posts though. You just can’t create them.