Gargle with salt water. It does the job.
Too clarify, I don’t think mouthwash, gargling, or sinus rinces will stop an infection once it’s started.
If the virus hasn’t yet found an ACE-2 receptor, then yes.
Once started, it might be able to slow down an infection and give your body more time to ramp up. But once a cell sends out a few thousand copies of the virus all bets are off on whether something as simple as this can make a meaningful impact.
Put a drop of oregano oil under your tongue. It will make you hate life. But I’m told it is a natural antibiotic. Sure tastes like death.