In only a very few cases with specific degenerative diseases.
For the other 99.9% of us, the number of studies showing the difference made by exercise, healthy eating, not smoking or drinking alcohol are too numerous to mention.
Ignore the information about exercise at your peril. You can probably use motivated reasoning to convince yourself you are right to remain in your chair and your growing list of ailments have nothing to do with your lack of exercise, and you may even remain convinced until you die. That will not change the opportunity you miss to enjoy decades of better health and life.
To grossly oversimplify it, our bodies literally evolved over billions of years to exercise and rest, eat so we are alternately storing excess energy as fat and removing energy from fat stores, and only eating sugars, alcohols, and inhaling smoke as extremely occasional events. I it stupid to assume switching the routine to sitting most of the time, only storing energy as fat and rarely if ever depleting those stores, and frequently consuming sugar alcohol and smoke would make no difference.
I could regale you with pages of personal experience (fmr intl-class athlete, trained and sedentary for periods of life and observed results) and data, but those are easy enough to find. All I can do is encourage you to change your POV, and start exercising well
You will find the 'built different' is how you build your own body —— weight lifting isn't called "body building" for nothing —— it (along with running and stretching) really does rebuild your body over the course of months.
Good luck and I wish you well on your journey.