check logging is on (should be):
/usr/libexec/ApplicationFirewall/socketfilterfw --getloggingmode
check logging option:
/usr/libexec/ApplicationFirewall/socketfilterfw --getloggingopt
mine said 'throttled', so:
sudo /usr/libexec/ApplicationFirewall/socketfilterfw --setloggingopt detail
check logging config for subsystem:
sudo log config --status --subsystem com.apple.alf
likely says "Mode for 'com.apple.alf' INFO PERSIST_DEFAULT" so:
sudo log config --mode "persist:info" --subsystem com.apple.alf
now use log(1) like
log show --predicate 'subsystem == "com.apple.alf"' --info --last 1h
I do get some log entries when expected but they all have the same useful message "<private>"