Cars, dogs, coyotes, raptors, other cats, and disease are already threats that should keep your cat inside.
Add onto that the threat an outdoor cat poses to the environment and to its owners (e.g. toxoplasmosis), and there are overwhelmingly more reasons to keep a cat inside. Covid-19 can't tip scales that are already flattened in one direction.
Just be aware this is a cultural judgement. In the U.K., many shelters will not adopt out cats to people planning on keeping them inside, as it is deemed cruel.
I live in the US with 2 indoor cats, and don’t let them out for the reasons you mention.
However, I understand the other side of the debate also. We do a lot of work to ensure our cats get enough stimulus.
I'm aware different cultures have different attitudes toward the problem of outdoor cats. As a species, they're in a weird semi-domesticated state, so perhaps more intentional domestication is the solution.
However, that doesn't change the objective reality that they are in more danger (and cause more harm) than indoor cats. People who adopt cats should accept the extra responsibility and work of keeping them indoors, as you have. Thank you for being a good cat owner.
Add onto that the threat an outdoor cat poses to the environment and to its owners (e.g. toxoplasmosis), and there are overwhelmingly more reasons to keep a cat inside. Covid-19 can't tip scales that are already flattened in one direction.