I am not aware of where to find out what each update fixes, but when you use dnf it displays a list of packages to be updated so you can see the exact package and version being installed before you tell it to continue.
I know the maintainers document the updates but cannot tell you a specific location. Since each package group usually is maintained by different people there likely are lots of places to look for the details.
Since each package is separately maintained the numbering is not always consistent between packages, although when the packages are related they usually have the same version numbers, such as video drivers, libreoffice, etc. Libreoffice has several related packages and they usually are all updated at the same time with the same version number, as are kernels, and other package groups that are closely related.