AppCfg will become unavailable for download on July 30, 2020.
For appcfg commands you have to Migrate from AppCfg to gcloud command line.
But this link returns 404: https://cloud.google.com/appengine/docs/standard/python/tools/migrating-from-appcfg-to-gcloud
And will pycharm appengine support also migrate soon?
Apparently the link has been already updated, please try this one:
https://cloud.google.com/appengine/docs/standard/python/sdk-gcloud-migration
Regarding PyCharm App Engine support you'll have to check in JetBrains documentation.