VMWare Workstation on Ubuntu: Can't "see" windows server image in 2019 ISOs
Solution 1:
This message is not anything to do with mounting iso images specifically.
I see you are using Packer here, where the approach is to copy an AutoUnattend.xml containing the required settings onto a floppy image and then mount that.
I would check that there’s a section of this file that points to a valid Edition of Windows (e.g “Windows Server 2019 SERVERSTANDARDCORE”) and that if you are using Evaluation media which you appear to be, you do not supply a Product Key in the same file. The product key can be uncommented for MSDN and Retail/VLK images.