If you want to use full Windows 7 and Windows 8.1 you will need a paid license and disk.
This is an Virtual Machine in OVA format that basically downloads the evaluation version of the Windows version you select to one drive as installation media and then installs onto the other (primary) virtual drive.
You can get the older official virtual machine images for Windows 10 here for testing
1. MSEdge.Win10.VirtualBox.zip is official from MS, VirtualBox image for testing their Edge browser (password for the user is Passw0rd!)
2. Windows10vm.7z is another build that logs in automatically (no password) and includes a snapshot on the install date so it's always possible to restart the VM at day count 0.
Both images are limited to 90 days
You can get official virtual machine images for Windows 11 here for testing