Please eliminate sandbox restrictions while running in Docker
Right now the sandbox applies to azure function apps even when they're running in docker. Docker is the sandbox in that case. Further, things like System.Drawing.Common aren't effected on Linux the same as they are on Windows so there should be no issue requiring the sandbox to interfere.
So Azure Functions should disable the sand-boxing when running in docker entirely.
Failing that, it should disable the System.Drawing.Common limitations if running on Linux.
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