Unless it’s changed very recently, I think logo design is the most popular gig according to Fiverr’s slide thing a while ago. Logo design gigs seem to be ones that have the most reviews (all time). There are also some voice over gigs with many thousands of reviews.
You could also look at this from the Fiverr blog which gives some ideas about what will be/is in demand:
It’s might not be a good idea to create gigs especially related to the virus but they might ask for other things that might be related to it (like a video edited where they give info on it or like someone said, infographics about it) but they could be in more general gigs.
The gigs that sell the most/have the most reviews aren’t necessarily the best ones to create. The amount of profit per gig sold should also be taken into account as well as the amount of competition for those services. Also skills like said above. But some of the suggestions in the link above might help too.