Resolved: ostree 2023.4-2 (as linked in the comments below) has been pushed to stable, updating your system will resolve the issue.
Tl;dr: There seems to be a bug in ostree-libs 2023.4 that causes errors when trying to update flatpaks, gnome software loads forever when trying to update a flatpak and manually running flatpak update shows errors (I was getting an “input buffer too small” error, others seemed to be getting errors like “Need more input”.)
Running sudo dnf downgrade ostree worked perfectly for me, I’ll be ignoring the ostree/ostree-libs update for now and hopefully the issue will be resolved soon.
Fixed in this release: https://bodhi.fedoraproject.org/updates/FEDORA-2023-464fae1680
Just ran into this as well and the downgrade command also worked for me.
Quite disappointing that we keep getting terrible issues like these on Fedora every few months.
If someone were installing Silverblue today, they’d give up and go back to Windows.
More importantly, WHY CAN’T THEY JUST ROLLBACK THE UPDATE ASAP AAAARGH