Hello Navi, I am Henry and I want to help you with your issues.
The GalleryLocations value must be a String Value (REG_SZ), not a Multi-String Value (REG_MULTI_SZ) as shown in your image. The system only reads REG_SZ for this specific setting.
- Open Registry Editor (regedit) again and navigate to: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Virtualization
- Delete the GalleryLocations Multi-String value you created.
- Right-click in the empty space, select New -> String Value.
- Name the new value GalleryLocations.
- Double-click it and set its Value data to the URL: https://go.microsoft.com/fwlink/?linkid=851584
- Close and re-open the Hyper-V Manager. The Quick Create gallery should now populate.
Issue 2: Have you attempted to disable Secure Boot for the Linux VM?
Please let me know how it performs.