@Edent Not quite what you asked for, since I can’t yet give a personal recommendation, but I have had Listmonk (like Dan Q) above on my ‘want to try’ list for some time, along with https://github.com/ElliotKillick/rss2newsletter .

@Edent In case useful, I've used https://yarpp.com for related posts, and XYZ SMAP for cross-posting, for a long time.