I like Amperfy and I think Navidrome has a Subsonic API: https://github.com/BLeeEZ/amperfy

Seems to be the case of at least Biden, Trump and Obama’s bodyguards too: https://youtu.be/KX7f1PwXEWg

A similar alternative to Pairdrop with a chat UI: https://drop.lol/

Yes you can achieve this with Pocket or Wallabag, a FOSS alternative.

Wallabag also have an automatic tag feature that can add tag based on the URL, so it would be possible to make different reading lists as you suggested: https://doc.wallabag.org/en/user/configuration/tagging_rules.html

Which type of content are you after? I have a page where I curate nice pics on the fediverse. There is some nature photography, but not only: https://kevinronceray.com/notes/pixelfav