Hello Muhammad
The next-hop IP address used in BGP is always that of the source of the BGP information. This means that whenever the next-hop-self feature is used, the router replaces the next-hop IP address of the route with its own IP address, and specifically, the IP address which is used for the BGP peering. If that is the loopback address, then that is what will be used.
I hope this has been helpful!
Laz