Really? On every team I've worked since the media query and bootstrap days, it's been normal to have a mobile, tablet, and desktop version at least. Tiny phone and ultrawide were bonuses, but having at least the basic three meant a somewhat usable experience for everyone.
These days it's even easier with MUI and similar UI libs that have responsive components built-in. Tailwind also makes it very easy to build your own.
Technically, that's correct (which means it's the best kind of correct).
But... I'd add that doing that well isn't easy. I frequently find cases where the mobile version simply removes features the desktop version has. And tablet version are very very rare. They tend to be either just the desktop or mobile version. Rarely is someone designing for tablet.
And that makes sense. Designing 3 different sites to all be the same feature-wise isn't trivial. Then you throw mobile apps on top of it, and suddenly it becomes much harder.
Can it be done? Sure. But I wouldn't say it's trivial to do it well.
These days it's even easier with MUI and similar UI libs that have responsive components built-in. Tailwind also makes it very easy to build your own.