Hi @MT,
Sorry to hear that your VM is not booting after performing an in place upgrade to Ubuntu 20.04. For future updates we recommend deploying a new VM with the required OS and migrating your data.
It appears that there may be some issue with the grub installation. I recommend attempting to use the Azure Linux Auto Repair script. This addresses many of the common configuration issues with the VM. Instructions for how to run this and other repair scripts can be found here.
Hope this helps! Please let me know if this resolves your issues.