Cant speak for the beta's but Apple's Supposed 12.4 fix for the exploit after disabling the feature didn't fix anything for myself and the one other person I used to use the feature with.
Picking the contact and sending invites from either party does nothing. No invite is sent or received from either end even though it shows the contacts walkie talkie card as greyed out with "Invitation Sent".
Tried resetting network settings, rebooting all devices several times, deleting the invitations and resending, changing the contacts phone number category from "mobile" to "iPhone" in the contacts app, logging out/in of FaceTime & iMessages, and even have completely reset and re-paired both Apple Watches. Nothing has worked.
Bummer we found it to be a pretty useful feature.