: Historically, Microsoft provided free virtual machines for web testing. You can check the Microsoft Edge VM Download Page for any remaining IE11 on Win81 packages.

: Community-preserved copies of official Microsoft ISOs and VHDs are often hosted on the Internet Archive . Use these with caution and verify file integrity if possible. How to Create a Windows 8.1 VHD from an ISO

While Microsoft has officially ended support for Windows 8.1, users can still acquire (Virtual Hard Disk) files for testing, development, or running legacy software in virtual environments like VirtualBox or Hyper-V . Direct Windows 8.1 VHD Downloads

If a direct VHD download isn't available, the most reliable method is to download the and convert it or install it directly into a virtual disk. YouTube·Peyman Tech Media Install Windows 8.1 on Virtual Machine using Hyper-V