Does diet affect the occurrence and severity of pain?

Many swear by a Keto style diet. No carbs and no sugar. They say it fights inflammation. It may help. Our bodies are so complex its hard to say what might be a trigger in one person. I dont think diet is the answer for everyone. White potatoes are not a good choice on Keto. sweet potatoes have fewer carbs. Cauliflower potatoes even better. But like you I love mashed potatoes and gravy.

a google search will keep you busy. Even an old thread from this site. The keto and non keto are almost like republicans and democrats in their beliefs. Here was an excerpt from NIH.

Background: A low-carbohydrate ketogenic diet has been reported to improve chronic pain by reducing inflammation, oxidative stress, and sensitivity within the nervous system. The main aim of this trial is to evaluate the effects of a ketogenic diet on reported pain, blood biomarkers and quality of life in patients with chronic pain.

Don't eat it if it is white - this is what a doctor said to me decades ago and it is some of the best advise I have been given. Sugars and carbohydrates feed inflammation. White rice and white potatoes are pure carbs, refined sugar is a big offender. Dive into a balanced diet and possibly look into a diabetic diet to help eliminate sugars. Your PCP might be able/willing to help with guidance.
I gave up white foods years ago then gave up refined sugar 2 years ago. I always argued that chocolate cake was not white. I no longer even want foods with sugar, it is no longer appealing. I will admit to some withdrawal initially, it only lasted about two weeks. I have always liked veggies and fruits so it was not difficult for me. While withdrawing sugar I did eat more fresh fruits to replace sugars. That declined and now my fresh fruit is about 1-2 servings per day. Also, I am a breast cancer survivor so I went organic at home 25 years ago. I am a firm believer you are what you eat. If you want to put artificial flavor, colors, and preservatives in your body - go for it, just not me.

SUGAR! (for me anyway)
And as already reported, we all draw the line at different points.
I rarely eat bread but I eat potatoes occasionally. I drink orange juice and fruit smoothies. But definitely refined sugar, always results in pain. And it takes surprisingly little

I choose to believe the other half of the story of diet is, ... is that the healthier and more efficient my body is, the less suspectable I am to flares, and they last less time. And combined with even a minimum of activity or exercise, the body can function better than, .......... If I don't.
Herbs can help too. Collagen powder contributes to muscle health. And I choose to use a specific strain of Kratom, which is the ONLY thing I have found that relieves flares within 30-60 minutes with no side effects. That strain can be purchased through the Mitragaia website and the strain is called "Super Green Malay"
But everyone responds to herbs and supplements differently and this is a very personal decision.

I will go way out on a limb and say "diet" is not isolated to what we eat. There is a certain level of accompanying acts and even attitudes that are what we feed our body to improve the quality of life.
For me the key element to try to feel better and do better is kindness. Consciously being kind to myself. And not looking at my body's condition as an adversary or enemy. Kindness to myself comes from extending kindness to others.

I know this seems like I strayed off topic for what food can kick in PMR. But what doesn't work or what hurts us, that we have control over is just half the process

I am a registered dietitian and eat a primarily plant-based, whole foods, organic diet. I experienced a short bout (about a year) of PMR following my second COVID vaccination and never had elevated inflammatory markers, so it took 4 months to diagnose. A keto diet can be helpful with some medical conditions and it will help with weight loss in the short term, BUT it is not healthy as a long-term diet. I feel that the primary nutrient lacking in the ultra-processed standard American diet (SAD) is fiber. Fiber not only feeds your gut microbes, which is essential to your health, but it also comes with many more nutrients since many nutrients are processed out or are located right under the skin/peeling of foods. I eat potatoes often, but they are the small ones with their skins intact. The larger the potato, the less skin per calorie and most people peel the skins off. Be sure that you only eat organically grown potatoes or you will be eating fungicide, as well.