Trump ran a personal account (from which he was permanently banned) and the Seal was often displayed there. Prove me wrong. All Trump's non White House tweets are archived.
I don’t know if it’s a Facebook policy or a Biden administration policy. So far as I can see, the archive of President Trump’s personal tweets is text (and emojis) only. I could be wrong. There could be another archive somewhere. But the vast majority of Trump’s personal tweets do appear to be text only, so pictures of the presidential seal would have been unlikely to come up in his non-official account. It’s likely that Trump did many or most of his tweets himself, and staffers are doing them now, so it may have been in the guidelines they were given.