As you can see it has an HDMI and a micro usb connector. So far for pure rendering I have connected HDMI to my R-PI and micro USB via an adapter to 5V/GND external power. Like this the R-PI never went into under voltage because it did not have to give roughly 0.5A to the LCD.
Problem: Touch screen works only via the micro usb adapter, when connected to the USB port of the R-PI. This means that I am now taking the 0.5A from the R-PI instead of the external power supply. This regularly causes short periods of under voltage on my PI-4.
Idea: Use a micro USB breakout at the LCD, a regular USB breakout at the R-PI. Connect TX and RX and FWIW also 3.3V accordingly, but take 5V (and maybe GND) of the LCD breakout from the external PSU and leave them unconnected at the R-PI (at least 5V).
Note: R-PI is also powered via the same external PSU, so they are referencing the same ground.
Is this feasible? Are there better options?