Just a few quick notes in case it helps anyone...
I've had a Win7 64-bit VM since 64-bit Win7 VMs started working well in VirtualBox -- I set the VM to dual-boot Win10 when the very 1st beta was released. It's been a while. Well, Microsoft finally pulled the plug on updates to Security Essentials, plus I hadn't used it for anything but helping to compact its Win10 sibling every patch Tuesday, so I figured it was time. Upgrading it to Win11 would make it useful again.
VirtualBox does support Win11 *legally* -- it emulates the needed secure boot & TPM etc. -- but it was a royal PITA getting an existing Win11 VM switched over to the V/Box version 7 that included that stuff. I wasn't going to bother with that this time. I had read that Microsoft tightened up a bit on the hacks allowing Win11 to install on unsupported hardware, but replacing appraiserres.dll still works. That's the file in the Windows setup files that does the hardware checks, and replacing it prevents [at least most of] those checks from happening. The original hack called for replacing it with the file from Win10 v.1809, which is what I did, but from what I've read, many people use an empty .txt file, renaming it appraiserres.dll.
The upgrade actually went fast and smooth, but the result was not nearly as nice as upgrading Win10 to 11. The biggest problem was the Start Menu... while the upgrade will Not let you keep any software you've got installed, it did keep quite a few of the Win7 Start Menu shortcuts and folders, at the same time not adding every one of the Win11 shortcuts I've seen in other Win11 installs. But it's working.