Keycard applet runs on any JavaCard 3.0.4+ (see applet installation)
We use for manufacturing:
model: NXP JCOP4
interfaces: NFC, ISO7816
EAL6+ certified
MCU: STM32H573
interfaces: 12-key keypad, power button, TFT color display, camera, smartcard reader, USB-C
battery: replaceable BL-4C 800mAh battery
flash map: 2MB dual-bank flash, with 32KB bootloader + 608KB firmware + 384KB data per bank
more details: hardware files, schematics, and firmware sources are in the Keycard Shell repo.