TLDR; This turned out to be a disk I/O starvation problem. You can leave your VM at 4096MB as long as you have decent fast disk to run from.

TLDR; Give your VM's 9216MB of RAM instead of the default 4096MB

Just spent an hour or so trying to install F41,42 and U2404,2504 on Hyper-V on Windows 11 Enterprise the performance was terrible

Fedora 41 Boot loader wouldn't install and the other just responded like treacle to every stage and I couldn't get the OS to install after a very, very slow boot to a GUI

I thought maybe it's because I recently Bitlocker encrypted C: and D: (The volume I'm running the VM's from) and that D: is a 5400RPM 6TB drive which doesn't help with performance

It didn't seem to be CPU as Hyper-V was only reporting single digit CPU % . I have a AMD Ryzen 9 3900X 12-Core Processor, 3801 Mhz, 12 Core(s), 24 Logical Processor(s) which should still be performant enough and 32GB RAM on the host.

The solution was to up the RAM from 4096 to 9126 (4GB to 9GB) and now the installs are running and I am booted into both VMs with acceptible performance

I also disabled Secure Boot in the Hyper-V VM settings and disabled checkpoints to help with performance too.