So I’m guessing the other TBRs are shown because they respond to mDNS discovery with the Thread network info (_meshcop._udp) and I’m also guessing you can’t make Apple your “preferred” network because the iOS mobile companion app doesn’t yet sync the thread credentials dataset, and you can’t provision new devices without that.
I noticed the latest Android companion app now syncs Google’s Thread mesh credentials to HA, so I wonder if you can make that your preferred network after syncing, has anybody tried it?