DPT: Are custom environments imported by default?

I just exported a project where we use a custom python-environment for faas. After import the imported functions are already using this environment, however when I click on change environment I cannot select the custom environment.

Looking at the export-ZIP there is a json functionEnvironmentsMeta.json, that holds some meta-infos of the environment. However I am not sure if the environment is really exported and imported and ready to use.
Does someone have experience with this?
Best Pernulio