Due to the prevalence of Community Applications, starting with 6.10, the template repositories page doesn't exist at all.
Your options for this are https://forums.unraid.net/topic/112170-allow-template-repositories-to-be-hosted-from-other-sources/?tab=comments#comment-1021630
In other words, Gitlab support on template repositories will never happen. For stuff to be published for the Apps tab it's not a hard "no", but would need to be investigated