User with Service Access only can't retreive Opportunity

I have a User, WFSRVUSER, that I am setting up to use in my Octopus API calls. I was able to create a PAT for the User through Octopus and I have assigned only Read permissions in the access rights.

We have tested the PAT and can Read AbEntry, Case and Schema, but not Opportunity. It returns empty. When I use the same request body, but substitute my own PAT, the request works and returns the record.

Is this a Bug or something on my end?