Found 2 bugs:

SaaS:

When creating a new service, there is no option to use OIDC authentication method.

Workaround: Create the service then edit it, the option will be there

On-prem:

Steps to reproduce

1. Create new service
2. select nginx
3. select OIDC
4. Press the button "Create service"

Issue: Service cannot be created with following error message:

 Couldn't create service. Check your Plan limits

Expected:
Service is created and OIDC is set as authentication method