If you turn on logging for a zone and add a log limit in advanced settings as described here: https://openwrt.org/docs/guide-user/firewall/fw3_configurations/fw3_traffic_logging, you can get an error.
root@device:~# fw4 print > /tmp/fw4print
Section @zone[0] (lan) option 'log_limit' is not supported by fw4
This is from v 22.03.2