Weather there are some Networks in Address List or not, in this dropdown there ist always the word "unknown" in the menu.
See in Attached Screenshot.
Probably you do not have an IGP route for your local prefix. In RouterOS v6 there was a synchronize option for BGP networks, where you could set synchronize=no or synchronize=yes. The option is now fixed to synchronize=yes and cannot be changed, so you won't advertise the prefix unless you have a local IGP route for that same prefix as well.Same issue here but still no luck to solve and back downgrade the version from 7.1 to 6.49.2. my local prefix was not working advertised via BGP Network in version 6.49.2.