I got the most help from a Dermatologist that has tried everything for this. She cultured my mouth and nothing significant showed up...just normal mouth bacteria. I had a really bad metallic taste in my mouth and she recommended getting my B12, Zinc & Iron checked. My B12 was very low. I have been on B12 shots now for 2 months which has removed the metallic taste in my mouth. (Look up low B12). You can also get glossy tongue from low B12. Go under Google Scholar and type in hypersalivation after Covid. It mentions thrush and then angular chelitis and hypersalivation. I had a bad case of thrush with Covid and then the hypersalivation (thick slicky saliva) started after the thrush cleared up. I have tried everything and nothing has really helped. Listerine works for a little while daily. I also use Peroxdyl (Colgate) once daily. It has peroxide in it and will bring to surface on your tongue all the excess and you can scrape it off better with a tongue scraper. Have you tried an over the counter antihistamine? They help, but, IF you have dry eyes already like I do, it will make them worse. Certain foods make mine worse such as pizza. Is it the tomato (acidic), cheese (dairy) or sodium? I don't know and I try to steer clear of pizza. I've battled this since last October. Some days are better than others. I am praying for you as it is an ordeal. God Bless You!