Grsync Flatpak Request

It’s been years. But I can’t find a single, user friendly application on GitHub that would allow me to copy Pictures folder incrementally to a USB drive on a monthly basis. Pika Backup and Deja Dup/Gnome Backup both create a sort of chunked archive that you can only access via those apps or a Borg client. That’s not an option for me. I want to be able to plugin the drive on any kind of system, and see my photos. No application can do that. Not on Flathub. GRsync can do it. But hard to install on something like Bluefin, Bazzite since they are immutable.