2.6 release notes say:
"Wildcard router component has been removed. As OpenShift 4.1 no longer has wildcard routes, 3scale 2.6 stops using this feature. We suggest replacing wildcard routes by creating specific routes, one by one."

They can be created manually, but that's not ideal. Instead, in 2.6 Zync takes care of creating those routes automatically. Documentation to this should be linked from here instead.

• templates https://access.redhat.com/documentation/en-us/red_hat_3scale_api_management/2.6/html-single/installing_3scale/index#onpremises-installation
• operators https://access.redhat.com/documentation/en-us/red_hat_3scale_api_management/2.6/html-single/installing_3scale/index#deploying-threescale-using-the-operator