> I've heard from people who have worked with the Signal foundation that it was close to being endorsed for private communication by one branch of government, but that endorsement was rescinded because another branch didn't want people knowing how to stay private.

The US government recommended Signal to for personal communication. See this article, in the section "Signal in the Biden administration and beyond":

https://www.snopes.com/news/2025/03/27/biden-authorized-sign...

And here is the government publication:

https://www.cisa.gov/sites/default/files/2024-12/guidance-mo...