It's getting very hard, since lots of modern cars don't have space behind the dash for a head unit, since their infotainment screen is now not commonly attached to the amp.

If your car has space for a head unit, and a fascia is available, and a steering wheel controls adapter is available, and a backup camera adapter (sometimes eight needed for the cars with "birdseye" view systems), and a climate control adapter, and sometimes a navigation system adapter, you might be able to seamlessly install a headunit. It just might cost a lot.

For most modern cars, it's a pipe dream.