None of those is correct, but the nearest one is #2. It should be: "When Covid 19 started, we stayed at home." 'When Covid 19 started' refers to a single point in the past. This is why you need to use the past simple ('started'). This phrase is your time reference. The main part of your sentence, 'we stayed at home' should also be in the past simple. This is because the two events were simultaneous, with the first event causing the second. When we have two events which are related in this way, they both need to be in the past simple. I hope that helps.

hi :) they all are correct grammatically. you used simple past , present perfect , and past perfect. The meaning they convey is different though...

Hi You don’t need the “had” or the “has”. When Covid 19 started, we stayed at home.