Inventory first
Before choosing a replacement, walk the car's systems and write down what runs through the factory unit: steering-wheel controls; the reversing camera and any 360 view; parking sensors' display; the factory amplifier and its tuning; climate or vehicle settings shown on the screen; warning chimes; the microphone used for calls and voice control. Each item is either preserved by the new installation, replaced by an equivalent, or consciously given up — the failure mode is discovering one afterwards.
The three replacement routes
Vehicle-specific unit: developed for the car's dashboard and integration; the highest preservation rate and the closest-to-factory result. Universal unit with integration parts: broader and cheaper per car, with preservation depending on the decoder and harness specified for that vehicle. Keep the factory system, add capability: a CarPlay adapter if the car has wired CarPlay, or a portable screen if it has nothing — no functions are risked because nothing is removed.
Questions that protect the outcome
Ask, for the exact car: which documented functions does the recommended unit preserve? Does the factory camera display, and at what point in the shift sequence? Does the factory amplifier stay in circuit, and who tunes it? What happens to vehicle settings that lived on the old screen? A seller who answers these per vehicle, in writing, is selling a replacement; one who answers generally is selling a box.
A note on older and newer cars
Older cars are usually simpler: less integration, more aperture, fewer surprises. Newer cars concentrate functions in the screen, which raises both the value of a correct vehicle-specific unit and the cost of a careless one. The inventory habit is what scales across both.