iphone – How to retrieve the real physical screen DPI/PPI on iOS to draw a rectangle with an exact physical size?

I’m developing a Delphi FMX application for iOS and I need to draw UI elements with a real physical size, for example a rectangle measuring exactly 3 cm × 3 cm on screen.

On Android this is relatively straightforward because DisplayMetrics exposes densityDpi, but on iOS I only see APIs such as:

UIScreen.mainScreen.scale
UIScreen.mainScreen.bounds
UIScreen.mainScreen.nativeBounds

From what I understand, scale is only the logical Retina scaling factor (2x/3x), not the actual physical PPI/DPI of the display.

Questions:

1. Is there any public iOS API to retrieve the real physical screen PPI/DPI?

2. If not, what is the recommended way to draw UI elements with a real-world physical size (cm/mm)?

3. Is maintaining a device-model → PPI lookup table the only solution?

4. How do professional iOS apps handle this problem?

Example:

// Goal: draw a rectangle exactly 3 cm × 3 cm

I would appreciate clarification on the recommended iOS approach here.