How are end-users and devs supposed to know about new releases?

Both answers so far require proactive behavior on the part of the user to go out and periodically check for new releases. That's not what I asked for.

An announcements mailing list would be great, but the old OpenWRT announcements list was shut down in the last year or two.

I don't use twitter myself, but that would be reasonable. However, the OpenWRT official twitter account doesn't appear to list any announcements, and is also full or non-announcement kind of self-promotion that would be inappropriate for an announcements mechanism.