Lime (the garden kind not the fruit) over the shit is best, sawdust is also good, woodstove/fire ashes, or dirt if nothing else is available. If there are flies, you need to use more of what you are using. A smallish shovelful of lime after every shit should be enough, a 50 lb bag kept dry will hold you for a while (months).
Wipe the seat with bleach diluted 50/50 with water, and you should be good, BUT if you are sharing a shitter with folks with COVID-19, you are probably living close to them, so you are going to get infected, regardless of toilet seats. If they are virus negative, normal cleanliness will be fine.
If folks of doubtful status share the shitter, but not your living space, you should wipe any surface they could have touched before touching it.
This is a respiratory disease, and folks' butts are the least of our worries right now. It's their coughs, and their breath, that we need to be scared of.
Try to allow some time in between uses, but if there are a lot of fecal aerosols, folks are probably already going to do that.