Yep. I used a navage (even though I hate their incessant commercials) when I had covid. It actually makes sense to try to flush out the excess mucus. The immune system can get to the internal parts of the body but if the virus can exist as a vector in mucus then it persists longer near but external to your tissues, from which to keep trying to re-infect those tissues.
Same. Had a very mild case.
Works for seasonal allergies as well.