Hello Thank you for your question and reaching out. I can understand you are having query\issues related to Mount of .vhdx image.
- Disable any Antivirus program or Windows firewall you may have for temporary purpose.
- Reboot your PC
- Go to Disk Management -> Click on Action -> Attach vhd -> Select path of .vhdx file -> Tick on CheckBox ReadOnly -> Click OK. --If the reply is helpful, please Upvote and Accept as answer--