Where else do you suggest they post? Publishing to the socials casts the widest net form them. If they operate their own website and post there, a number approaching zero would see the posts.

Do you expect a new app per municipality to be a solution? Or one app to become a new platform just to interact with gov't agencies that the other platforms already provide? You have the question, but have you spent any time coming up with answers/suggestions?

In Norway most withdrew from X. Norwegian police made a webpage, an rss feed, some push system and an API. So others have made bots that repost on various social media, but the source is no longer in a walled garden.

Multi-publish is a thing that is managed by numerous publishers. Right now, most govt sites ime no longer publish at all on their sites or rss but instead update one of facebook or twitter, depending on their preference. If they can afford to buy 70k usd suvs at taxpayer expense, they should also be able to figure out how to publish on mechanisms without walls, such as rss or their own site.

My locale uses Nixle to send people alerts: https://www.everbridge.com/products/nixle/

A municipal website? A text file on a file server? Not a login-gated social media platform owned by the world's richest edgelord.