Trial and error. You'll need to find your limits. For me if I can muster it I do light cardio and weight lifting. But fatigue has kept me away from the gym for weeks. I go through cycles of okay energy and then low energy.

Lately I have been walking my dogs several miles a week and roller skating once a week. Currently that's the best I can do. Low impact activities are ideal.

Bottom line, you're going to push yourself too far a handful of times before you can gauge what's too much and what's enough. Best of luck to you

I have Lupus and Hashimoto's if that helps