I have published a Map Service and associated Feature Service (feature access to enable editing) off my enterprise geodatabase. It results in a Map Image Layer and Feature Layer in my federated Portal. The Feature Layer points to server API resource (.../FeatureServer) and the Map Image Layer points to server API resource (.../MapServer).
I have tried to share the Map Image Layer publicly while keeping the Feature Layer just accessible to me for editing purposes (see screenshot)

However, if I navigate to my REST endpoints on server as an anonymous user (using an incognito window to ensure no credential caching), I can see both the MapServer and FeatureServer

What's more, as an anonymous user, I can query and edit the features via the Feature Service API endpoints (delete, add, etc).
We are working on a fully patched 10.9 Enterprise with federated Portal. This seems like it is not working as designed, and it also seems like I can't be the first person to experience this if its some undiscovered bug.
Is there anything I could be doing wrong / anything I'm missing?
It really seems to undermine the security of the entire system if otherwise.