macOS Catalina 10.15.7 stuck while installing

[ReynierP]

I have an iMac Late 2013 and therefore Big Sur is not supported (sadly for me and many others ). I would like at least to test Big Sur in a Parallels VM but I am unable to install Catalina 10.15.7 so I can upgrade inside the VM. How I can install Cataling properly inside the VM?? See the attached screenshot for more info

 

[RichardB44]

This is a pretty late reply and I'm sure you have it working by now, but for others following the same path...
I had this issue upgrading macos 10.14 Mojave to 10.15.7 Catalina in the VM, and it hung indefinitely as in your screen shot.
I fixed it by disconnecting the VM's network (menu bar Devices -> Network -> Disconnect) and rebooting. Then the upgrade screen appeared again but this time the thermometer was moving properly and it was showing the time remaining (which was now counting down).