CentOS 8 ships only with iptables-nft (ie without iptables-legacy)
The only tested configuration for now is using Calico CNI
You need to use K8S 1.17+ and to add calico_iptables_backend: "NFT" or calico_iptables_backend: "Auto" to your configuration
If you have containers that are using iptables in the host network namespace (hostNetwork=true),
you need to ensure they are using iptables-nft.
An example how k8s do the autodetection can be found in this PR