In PPSSPP, go to Settings > Networking . Tap Change PRO ad hoc server IP address and then tap Toggle List to see your local IP (usually starts with 192.168... or 10... ).
This is the most stable way to play with friends in the same house or on the same network. adhoc server ppsspp
A $35 Pi Zero 2 W can run an adhoc server 24/7 with minimal power. Install Raspbian, compile the server from source, and run it as a service. In PPSSPP, go to Settings > Networking