RE: Big Sur
FYI, I just spent hours chasing this down. The board wasn’t showing up under USB devices. Turns out that I was plugging into the USB 3.0 port on my MacBook. Switched to the port on the other side and the device showed up in this list of connected devices. Went back to PlatformIO and uploaded the sketch without issue. I didn’t need to change/add anything in the platformio.ini.
HTH