Remote Control – How do I know if my computer has been remotely controlled by an employer and monitored by it?

I'm working as a freelancer remotely, on a new Imac I bought extra for this gig. Until recently, I had a seat in the client's Adobe Enterprise and frequently exchanged files with the client. I became aware of suspicious activity, such as the cursor that moves on its own, and customers who relate to my work or computer activities they would not have known without access to my desktop or without mysterious system crashes. I have since tightened my security, but how can I detect the presence of a surveillance system or possibly an unused user and prevent access to my computer and potential invasion of privacy?