As acknowledged by the EEOC, employees with certain pre-existing mental health conditions may have a harder time dealing with the stress of COVID-19. As with any accommodation request, ask questions to determine if the condition is a disability and request medical documentation if needed. Discuss how the requested accommodation could assist and enable the person to keep working.
Explore alternative accommodations — which in this case and depending on your industry and workplace — could include changing their assignments to be more team-oriented, modifying their work hours to coincide with other team members, or determining if they could work at the office, taking into account the reduced contact requirements. Since the person is feeling isolated, encourage video chats instead of phone calls, more frequent check-ins with colleagues and/or managers, and engagement with your wellness or employee assistance programs outside of making a formal accommodation.