“What is a good natural mouthwash?”

5 Homemade Mouthwash Recipes to Improve Oral and Dental Health
Sage and salt mouthwash. Sage is on the top of the list of recipes to improve oral and dental health, because of its anti-inflammatory and antibacterial properties. ...
Salt and baking soda. ...
Herbal mouth wash ingredients 4 oz of peppermint and sage leaves plus Echinacea Angustifolia root.

This simplest would be the basic salt and baking soda rinse with purified water. You can also add a drop or 2 of you favorite flavored essential oil such as peppermint or cinnamon.

1/2 spoon of Baking soda
1/2 spoon of salt
1 Cup of water

I would personally recommend a mouth rinse with CPC as an active ingredient. Crest has a mouth rinse called “clinical” which has this particular ingredients. In times like this we need a good mouth rinse to kill viruses and bacteria.

It depends on what you are trying to achieve with your mouthwash and your current state of oral health and oral microbiome. Mouthwashes are a great adjunct to add an antimicrobial effect, relieve symptoms of dry mouth, or add additional fortification of your enamel, but it really depends on the person. The mechanical removal of bacteria and plaque by quality brushing and flossing should be the first priority, and then a mouthwash that fits your specific needs following that can be selected for your needs.
Thank you!