Snap is a proprietary format that is canonical-centric, don't tell me that the community make choice to make client opensource but official store both hardcoded (initially) and closed source.
On the other hand,flatpak is a freedesktop project, done using open standards like OCI and ostree.
No. Snap is not a proprietary format at all. It's a squashfs file with a small amount of metadata. You can make a snap by plopping a file in a folder, add a simple snap.yaml which describes the application and then "make" a snap with the common mksquashfs tool.
There is room in the world for flatpak and snap to co-exist. We created snaps as an evolution on from clicks on the Ubuntu phone, and it covers use cases that flatpak wasn't designed for.
On the other hand,flatpak is a freedesktop project, done using open standards like OCI and ostree.