Can you share re: your diet change?
Sure. The scummy plaque on your tongue is the result of poor digestion, which can be improved by reducing or eliminating foods and drinks that your gut biome don't like. Sugary drinks and alcohol are especially bad. Also by limiting the variety in your diet you build up the populations of gut bacteria that like those foods, which greatly improves digestion. A wide variety of foods confuses your gut as they are often too few in number for proper digestion of a smorgasbord of widely different foods.
Overeating also leads to poor digestion as too much food overwhelms the gut's ability to fully digest food, and properly eliminate waste. I eat two meals per day and snack a little at night so I don't go to bed hungry.
Your diet should be well balanced with protein, fats, carbs, and fiber.
I believe the best indicators of a good diet are,
A high level of energy throughout the day.
No hunger pangs between meals.
Little or no smelly flatulence (a sign of poor digestion).
Regular elimination, with no urgency, well shaped easy to pass stool, with little odor.
And of coarse a tongue free of bacterial plaque, and a clean smelling breath.
Edit.
Of course good digestion starts with thoroughly chewing your food, thus mixing it well with saliva, which contains the primary digestive enzymes. Food should be nearly liquefied by chewing. If the morsel is dry add a sip of milk or water to aid in the process. True hunger as well as the sight and smell of food being prepared promotes the production of saliva. Eating is both an art and science. Too often we wolf our food down, eat on the run, and often when we are not really hungry.
Unfortunately, many have dental problems that interfere with proper mastication of food. This must be corrected for optimal nutrition to be attained.