Update All: "Unable to update org.fedoraproject.Platform: Path does not exist"
Bringing this issue discovered on Silverblue: https://github.com/fedora-silverblue/issue-tracker/issues/145
I know Platform flatpak was updated to f34 just in that moment, so I can imagine some problem related to that.
Executing flatpak update
updated everything and the "Update All" button started to work again.