Did you follow the guide from militarycac.com? Even though you downloaded the certs, you may still have to go into keychain access and select to trust them. I’ve got an M1 and access those sites just fine. There are a few that require you to be on a NIPR network, but the main ones like DTS, AKO, DOD email, and things like that can be access on any network.
Just follow the guide‘s steps and make sure that all certs are enabled.