after removing the Public Access from an uploaded file and clearing all cache, then copying the URL link (and file name) to the browser, the file still shows on the public side. Are there TTL’s or other factors keeping that image publicly available? I’m not succeeding in consistently removing public permissions from files just via the removal of the permissions for that file.
Yes, there is a sort of "caching time". You might have already been aware that GCP has a very broad network around the world and it heavily utilizes caching system (CDN and similarities).
The documentation says:
By default, publicly readable objects are served with a Cache-Control header that allows the objects to be cached for 3600 seconds. If you need to ensure that updates become visible immediately, you should set the Cache-Control metadata for the objects to Cache-Control:private, max-age=0, no-transform.
So you have to set the metadata of object like that to remove the object from global caching system immediately when
publicRead is revoked :).