If you want to work for multiple customers, become a freelancer where you decide your own hours and ensure that there is no conflict of interest. Otherwise you are doing a disservice to your actual employer who expects your attention for the hours you are hired for, provides benefits like Health Insurance and everything else, trusts you that you will be there when they need you and in good faith expect you to not work for someone else at the same time.

Suddenly with remote work, this question has been coming up a lot and boggles my mind. How can someone do this in good faith ? ANother reason why fully remote work will be very tough for all employers.