@Richard_Littler Same here. I think it's far more common than is widely discussed (and anecdotally, I think possibly more common amongst neurodivergent people than the general population).
It's something I do try to draw attention to as much as I can, because it can feel lonely and othering when all you hear is 'exercise makes everyone feel great!'. Believe me, you're not alone in this. Many people don't feel good as a result of exercise and no change to the exercising will alter that.
I believe a current neuroscientific school of thought is that those who get the good feelings, dopamine or whatever, do so because exercise inherently feels very uncomfortable - shortness of breath, increased heart rate, sweat, joint strain - and the hormonal system evolved to disguise that unpleasantness in order to ensure that bodies got what they needed. Similar to how, if you need a particular nutrient, then food containing that can taste fantastic.
But it's a spectrum, as these things always are, and some people get all the euphoric feelings, and some people (you, me) get absolutely nothing except the unshielded discomfort, and others fall somewhere in the middle.