The rural areas I've been a part of tend to have one or more noticeboards, either on the main street, or often at the main supermarket. People put up flyers, business cards, possibly with links or qrcodes, or otherwise phone numbers.

In Vermont, there are mailing lists for every town that are widely used, https://vitalcommunities.org/community-discussion-lists/ and also Front Porch Forum https://frontporchforum.com/. I guess the latter is pretty much what you are talking about, a community social network that is not Facebook or Nextdoor and not trying to become a megacorp.

There is still a lot of facebook groups for many small towns, but its easy enough to totally ignore and just use noticeboards, ask/talk to real people, etc if you want.