@jdp23 @tokyo_0 The correct technical solution is as follows:
1. Get outbox endpoint from username: https://(instance)/.well-known/webfinger?resource=acct:(name)@(instance) .
2. In the body, there is a link whose "type" is "application/activity+json". Get that link, append "/outbox?page=true" in the end, then access it.
(Yes, if one is only dealing with Mastodon instances then https://(instance)/users/(name)/outbox?page=true suffices...)
See also https://github.com/RSS-Bridge/rss-bridge/blob/master/bridges/MastodonBridge.php which I wrote before.