A little bit of background.
Timeshift is in the Fedora repository but until some time ago, it was not updated since the times of the release of Fedora Linux 35. So it was not working and someone created a COPR repository with the latest (working) upstream version.
A non responsive maintainer process started some time ago and just recently another packager come up and took care of the package in the Fedora repository: currently the new package is in the updates testing repository.
I had a very similar issue on F36 today. I was updating the system and dnf would not do anything except telling me that the packages have already been downloaded. dnf clean all fixed it.
There may be some dnf bug be around.