NebLem

Outside getting people to join a fedi platform, Matrix instance, or Signal, all a non-trivial ask, you could see if they’re on Discord or WhatsApp already, which while neither is great at least its a step away. You could do a simple SMS group, if you are okay with the privacy risks - almost everyone still had a phone number.

Post mail surprisingly is still a thing too if you are okay with delayed messages and there being cost.

You can get the RSS feed and check it in a feed reader, for example for Sh.itjust.works you can use the feed https://sh.itjust.works/feeds/local.xml?sort=Active .

I’m not aware of any Lemmy app having such a feature though.