I just spun up a new CentOS 8 VM and ran the mandatory initial update and was rather surprised to see single packages downloading at 50KBps. I think 1998 would like their acceptable transfer speeds back!
It turns out that a couple of changes to your dnf.conf file will get you back into the 21st century.
Just edit your dnf.conf file:
nano /etc/dnf/dnf.conf
And make sure you have the following two lines:
max_parallel_downloads=20
fastestmirror=True
That’s all you need to get your package downloads speedy again.