Fabio: Based on what "upgrade" really means in the other post, you do not have the same problem.
About your problem: Do you mean that you are upgrading or reinstalling the Host? It is not clear.
Upgrade and reinstall are not the same things. You do not say that the Windows gets slow - only on VM gets slow. Is that so?
If so, and you did reinstall the Host, it means that your Cisco VM (which I'm not familiar with - what is it anyway and what does it do?) is somehow dependent on the Host. It IS dependent on the Host architecture and in this case - a bit far-fetched but the remaining explanation - it depends on the Host drivers. Did you say "I copied it" ? - if you didn't, you may have wrong drivers/connection to Host architecture/technology. That is easy to correct, just rename the VM directory and start it - and go from there.
If you have Nested virtualization with the Cisco-thingy, which you do not mention, then it is quite a different ball game.
According to my tests, Windows 11 Pro VM is always very slow, 2 times slower than the Host. But that hardly means unusable, if your Dell laptop is any good.