The FirewallBackend option selects the firewall backend implementation. Choices are: - nftables (default) - iptables (iptables, ip6tables, ebtables and ipset) The iptables backend is deprecated in favor of nftables, the modern default packet-filtering framework that firewalld uses.
Solution
Edit the file /etc/firewalld/firewalld.conf and add or modify the following line: FirewallBackend=nftables Impact: On a system already using the default nftables backend, no change occurs. Changing the backend from iptables requires a firewalld reload and rebuilds the active ruleset using nftables.