Wow, I've just discovered https://a.gup.pe/ - a mechanism that replaces the !groups functionality from the old identica/statusnet days.
Simply mention (AT)groupname(AT)a.gup.pe - for example @tzag - and that post will be boosted for everyone who follows that account.
(With apologies to everyone who follows @tzag! 😁)
Sorry if you already knew this, I only just discovered it.