I just verified with Vagrant that the necessary configs are working with CentOS 8. I had forgotten we do ship a newer mod_auth_openidc but it appears like I mistakenly did not include that in 1.8 repos. I think that’s the issue you were facing because the RHEL8 version of mod_auth_openidc is 2.3.7 which is too old to support OIDCStateMaxNumberOfCookies
I’d recommend updating to use the mod_auth_openidc shipped by OnDemand 1.8 repos:
dnf module disable mod_auth_openidc:2.3
yum update mod_auth_openidc