We cannot edit SPPB pages from the frontend when they are built directly in SPPB. Instead we get a 404-Component not found error.
We took a copy of a page that was built in the SPPB component and copied it to a Joomla articled, extended with SPPB, and then we can edit the page via the frontend.
Here's a video walkthrough:
https://www.dropbox.com/s/cwiaabvdr7tbykj/2022-03-10_16-52-30.MP4?dl=0