I have loaded my Gramps database to Gramps Hub but the media files in Gallery did not upload. I have a separate network disk with photos etc. I suspect I need to move all my photos, certificates etc. into the same underlying directory as my Gramps data.
The advice received was to create relative links to my photos folder. This did not work. So I copied all my photos that I wanted in Gramps into a single directory, remapped all the links inside Gramps to that one folder, made sure I followed the steps of creating checksums for all photos, and after loading my Gramps DB onto Grampshub, zipped the photo directory and uploaded it and voila, pictures in Grampshub worked. Trial and error!