An Apple ADB to USB adapter for QMK using the ATMega32U2, featuring USB-C! One of the projects I used as an intro to KiCad
Probably not the simplest, but follows what is said for the 32U2 datasheet.
Tested working, highly suggest a 32U2 with DFU bootloader flashed (DigiKey seems to have them preflashed) Highly reccomend using hot air instead of an iron.
You can use the online QMK configurator firmware builder to produce a .hex that can be flashed using QMK Toolbox (Arduino will not see the DFU bootloader!) (Or compile it locally and flash it however you want)
The CSV contains a BOM listing generated by KiCad, parts I used are listed below:
GRM0335C1E200JA01D (20pF cap),
CL05A105MQ5NNNC (1uF cap),
USB4085-GF-A (USB C port),
RMCF0805FT1K00 (1k resistor),
WR06X220 JTL (22 resistor),
ABLS-16.000MHZ-D-3-Y-T (16Mhz crystal),
M50-3530342 (optinal ISP headers),
PTS526 SM15 SMTR2 LFS (reset switch),
RR0816P-512-D (5.1k resistor),
WR06X103 JTL (10k resistor),
CUI_MD-40SMK (S-video socket) (yes, S-video),
and, of course, an ATMega32U2(-A)