Let the SharePoint Integration from Power Apps Portals use Subsites.
Currently the portal ignores all Subsites completly, but use custom Folder structures as long as they are created inside the main site and are created/associated before the portal can create them.

For example:

- https://.sharepoint.com/sites//Accounts/Folder1/Folder2
This would work in the current situation.
- https://.sharepoint.com/sites///Accounts/Folder1/Folder2
This wouldn't work in the current situation.

The SharePoint Integration inside D365 can use subsites, so it's not consistent between Portal and D365. This could lead to serious problems.

So please let the SharePoint Portal Integration use the same logic as D365 and enable Subsites!