in particular one comment as someone asked a similar question to you:
As per the terms of our license agreement, any use of the GitLab Software may only be used (i) for its internal use in connection with the development of Customer’s and/or its Affiliates’ own software. This includes GitLab pages. As such, based on my understanding of what you wish to do, I do not believe it falls within these parameters.
The way I understand that is no, it’s not possible. Gitlab as well as Gitlab pages is to be used for internal use with the development of your own or customer software. But it would be better for you to comment on that issue that I linked to get a definitive response, or I hope someone from the Gitlab team will reply to this post to answer the question or potentially updating the Gitlab Pages information to explain more clearly what is and what isn’t possible.