The gap
Three kinds of operating system — and you control none of them.
Whatever you run today is one of three, and each takes the floor away from you in its own way.
Shaped by a business model
The account you sign in with, the store you cannot remove, the telemetry you cannot see, the update you cannot refuse, the support that ends on a date someone else picks. None of it serves your job — it serves the vendor's revenue, and the forest of apps you must install is the product.
Free to read, still not yours
Even a free system is governed by the company that curates it. You inherit its package repositories, its defaults and its release calendar; you keep a plugin ecosystem alive; you live in dependency hell, where upgrading one thing moves ten others. Free is not the same as sovereign.
Hardware and software, fused
The sharpest case. The vendor welds the two together so tightly that you cannot run your own system on their device, and cannot have their device's abilities on hardware you chose. The user — and the designer — is closed inside a link neither can open.