The places I found a year or so ago don’t seem to be doing much information on diet but this is what I found. The best site right now seems to be the British National Health. I am not a dietician or medical person so I can only go by what I have found online and read elsewhere, but this gives a good start. I tend to favor the National Health Service as I don’t believe Big Pharma has any influence with them.

(This isn’t much help but is an example of the help I am finding now. The Mayo Clinic has good information)

https://www.whatispolymyalgia.com
Partially Hydrogenated Vegetable Oil like transfat and this can be found in fried foods and baked goods like cookies, pie crust, crackers, and pizza dough.

High Fat Meat and Dairy Products which triggers inflammation like bacon, lamb steak, dark meat, poultry skin, whole milk, skin milk, low fat milk, and heavy cream.
Low Fiber Starches worsens the symptoms of polymyalgia rheumatica as they stimulate inflammation. This can be found in white bread, low fiber cereals, and instant potatoes.

British National Health Service.

For Calcium: dairy products, such as milk and cheese, soybeans, okra, kale, spinach, sardines, salmon

Good sources of vitamin D include: cheese, fatty fish, such as mackerel or tuna, egg yolk, mushrooms, products fortified with vitamin D, such as certain cereals or bread (as long s they are gluten free)
Omega-3 fatty acids: fish oils, such as cod liver oil or salmon oil, mackerel, sardines, eggs, flaxseeds, flax milk, chia seeds, walnuts

Many foods have anti-inflammatory properties. Consuming these foods as part of a balanced diet may also help to reduce the symptoms of PMR.: tomatoes, fatty fish, berries, almonds, green leafy vegetables, olive oil

Foods linked to increased inflammation include: refined carbohydrates, such as white bread or white rice, fried foods, such as french fries, sugary drinks, processed meats, such as salami or hotdogs, red meat, margarine, foods with added sugar, alcohol,

Oils where heat is used to extract the oil, (and anything fermented like soy sauce, pickles, vinegar)
(Not listed are nightshade vegetables: Potatoes, tomatoes, egg plant, peppers, ground cherries, tomatillos, anything made with pork)
*Anything in ( ) are my words

My breakfast go-to is frozen spinach, cheese and scrambled egg. Thaw the spinach and mix in with the egg and add grated cheese to taste, cook as for scrambled egg- for me, I add a lot of cheese as I don't like spinach.

Simple chicken soup is a good standby. Chicken thigh meat, onion, mushroom, carrot, dried beans or frozen peas, chicken broth. Play with the recipe with simple spices like cinnamon or nutmeg for a richer flavour, and herbs like parsley, oregano. You can also add other ingredients from the lists above.