Trying to connect Microsoft Power Apps to a SharePoint Online library, specifically the Site Pages library ran into a little snag. Usually, when connecting to a data source you pick the site, then get a list of lists. Site Pages does not show up.
However, you can select the checkbox for the last/blank option, fill in “Site Pages” and proceed.

The connection should work just fine, and you can go about your Power Appy business.
don ‘t work….
Just tested and it still works for me. Are you connecting to a communications site? What issue are you having?
@wpreston: in my case I am connecting to a communications site.
When I try to enter “Site Pages” as you have shown in your screenshot, I get the following error messages:
Erreur
Nous n’avons pas pu ajouter votre source de données. Réessayez.
Réponse incorrecte du service ; le nom des métadonnées de la table pages du site ne semble pas correspondre au nom utilisé dans la demande de site pages. Contactez le propriétaire de l’API.
ID de session : [session ID]
Which in English is
Error
We could not add your data source. Please try again.
Incorrect response from the service; the metadata name for the site pages table does not seem to match the name used in the site pages request. Contact the API owner.
Session ID: [session ID]
If I try to enter “SitePages” or “Pages du site”, it says “List no found” instead, and a bunch of IDs.
9 months later, the same thing still happens. But I found a solution! Type in the ID of the library instead, that worked for me!