Yes! When creating Rescue Media, you can choose ISO File instead of USB. Save the ISO to your portable hard drive. You can then use tools like Rufus or Ventoy to make a bootable USB from that ISO. This is the most flexible "portable" format.
Macrium Reflect includes a built-in tool to create . This is a bootable Windows Preinstallation Environment (WinPE or WinRE) that contains a fully functional copy of Macrium Reflect. i--- Macrium Reflect Portable