My previous setup needed a level shifter to accomodate 5V logic of my receiver...

But most of radio today have a "buddy box" mode where they output directly PPM signal from the trainer port.

And these radios are today with 3.3V logic, like the ESP32.

So you can directly connect  the PPM jack cable to any IO pin of the ESP32. No more PCB, direct connection :-)

Schematics

Difficult to have something simpler...

Firmware

The firmware provided here on my Github is compatible with this 3.3V setup.

Simply be sure to uncomment this line