Errmm, I was talking about Updater.app, org.lineageos.updater, Version 16, which came preinstalled on my BraX3. It has a 3 button icon at top right, which exposes a menu with the middle item: Preferences. This exposes a panel of toggles, the bottom one is Show Beta updates I usually have this OFF. Two days ago following discussion in Iode' 7.7 BETA is out! I turned it on, refreshed, and it showed the 7.7 beta. Turned it off again, refreshed, and it showed no updates available. But there was no humanly visible indication at https://download.os-source.co/brax3/iodeos/v7/7.7/ that this was a beta.
This updater has worked perfectly for me downloading and installing the 7.5 and 7.6 final updates. I have not tried installing a beta with it.