Most insurers don’t class Covid-19 as a critical illness , so you won’t be able to claim if you get it. But, if you have Covid-19 and it develops into a critical illness covered by your policy, your insurer will pay out in line with their terms and conditions.
It’s a similar situation for income protection which is designed to support you if you cannot work because of illness. If you become severely ill because of Covid-19, you could make a claim for loss of income which your insurer will consider according to their guidelines. However, you probably won’t be able to claim for lost income if you have to self-isolate.