Hello jluyt,
AFAIK, "OPTIONAL" in this context means the parameter values are
not required at the time the blueprint is created (static) or at the time the blueprint is assigned to a management group (dynamic). If you uncheck the boxes shown below then you will need to enter a value. an empty set (i.e. []) is acceptable.
I Created a test Blueprint based on the "Enable Azure Monitor for VMs" Policy Initiative and was able to successfully save the blueprint without providing values for any of the 3 parameters. I was able to do this by checking the box "This
value should be specified when the policy is assigned". This means the value for the mandatory parameter (i.e. LA workspace) will need be entered at the time the Blueprint is assigned to the management group (i.e. subscription) and the other 2 optional
parameter values can be ignored (i.e. List of VM impages supported (Windows/Linux))
