I wrote a very simple configuration to select UPF based on S-NSSAI below.
[gNodeB(UERANSIM) x 1, AMF x 1, (SMF+UPF) x 2]
For each NF’s configuration file, the difference from the default configuration was posted, but as for the NSSF’s configuration file, I wrote the entire file.
You can trace the interaction between each NF and NSSF by getting a pcap file of this process and checking the SVG file created using 5G Trace Visualizer.
For your reference.