UFW & Iptables not working in Debian 10
If you are getting an iptables related issue generally or when trying to use an OpenVPN installer script or general VPN setup and the error is similar to:
iptables-restore v1.8.4 (legacy): couldn't load match `limit':no such file or directory
iptables v1.8.2 (nf_tables): unknown option "--dport"
iptables v1.8.4 (nf_tables): unknown option "--dport"
error: couldn't determine iptables version