Are you using Linux consumption? System.Drawing requires libgdiplus to be installed to run on Linux. It is not pre-installed on the containers used in Linux consumption. You can, however, put the function app into your own container that has the proper dependencies installed. Currently, custom containers are supported on the Premium and App Service plans. - Anthony
Yes, what you mentioned is right. You can use custom containers and deploy it to the Linux Premium plan.
Unfortunately, there isn't an ETA to share at this point. You can sign up for our private preview aka.ms/goazurefunctions and we'll keep this thread updated as things change. Thanks for your patience!
Thanks for the feedback. We’ll add this to the content backlog.
Thanks - we have added this to our backlog and will get to it soon.
This is something we are looking at but don't have plans for this yet. Please up vote if you need this, especially calling out the use case for the Az CLI if possible.