Should I overstay my non-immigrant O visa by one day to apply for a COVID extension, or cancel it first?

I doubt you're on ANY visa and instead are on an "extension of stay" <- read the line on stamp in your passport directly under the location of where the stamp was issued.

You get a letter from your uni stating you stop studying, you go to the immigration office that gave you that extension and cancel the extension. Then apply for a 60 day covid extension.

Letting an extension run out doesn't officially cancel it, :( that's not how it works :/