Hi @kados if not already installed, you should try the recent new version 1.34 of the OpenID extension. We were experiencing the same problem but after installing that one, it worked.
These are our settings from the xwiki.properties (I omit clientid and secret):
oidc.endpoint.authorization=https://accounts.google.com/o/oauth2/v2/auth
...
oidc.groups.claim=
oidc.idtokenclaims=
oidc.endpoint.logout=https://oauth2.googleapis.com/revoke
oidc.scope=openid,profile,email
oidc.endpoint.token=https://oauth2.googleapis.com/token
oidc.userinfoclaims=
oidc.endpoint.userinfo=https://openidconnect.googleapis.com/v1/userinfo
oidc.user.mapping=
oidc.user.nameFormater=${oidc.user.email}
oidc.user.subjectFormater=${oidc.user.email}
See also: Page load performance / Page Cache relevant? (which starts around another topic - page cache - but later in the thread there’s a lot about the OIDC extension).