I like Keycloak. It is very configurable, easy to set up, has lots of available examples of configs out there, and has been the most stable for me of any I've tried.
I only wish it had mock-LDAP so I could use it with things that don't do OIDC like OpnSense. Keycloak can use an LDAP server as a source and sync with it, but I don't want want to run a separate LDAP server for one or two systems. They're too much trouble to setup and manage.