The Amiga 500, 1200 and 600 had the keyboard in the computer, like the older 8-bit Commodore 64. Some Amiga fans have replaced the internal computer with a Raspberry Pi, connecting it to old internal keyboard and mice using a e.g.
Keyrah USB interface board.
There have even been new Amiga 500 and
1200 enclosures — with new mounting points just for the Raspberry Pi.
I have been brainstorming on a mechanical Amiga replacement keyboards, but never got far because I haven't been very motivated. One of many ideas was to have a socket for a Raspberry Pi Compute Module, so that a complete emulator could fit not just in a Amiga 500 or 1200 but also in the enclosure for an external Amiga keyboard.
I think this idea to have a RPi Compute module on a keyboard might be worth going forward with.
BTW, the Pi 4000 does not have a headphone jack.