Open-source boards designed in KiCad by SoCXin on GitHub, from 3 repositories. A board’s address here is its repository’s there.
SoCXin/GD32F350
L4 R4:GigaDevice Cortex-M4 108MHz MCU (GD32F350)
SoCXin/nRF52811
L2:Nordic BLE 5.2 SoC
SoCXin/STM32H730
L6 R5:ST Cortex-M7 550MHz MCU (STM32H730)