V2.1 - Bugfixes, improvements
Entering the menu can now be done by holding F1 or F5 in addition to the existing Up, whichever is more convenient. (BOOTSEL is now also on F3.) The keyboard routine is also more robust and less likely to misinterpret a bad keypress.
The low level SD card driver has been replaced, so cards other than the Lexar that comes with the PicoCalc should now work as well.
The bootloader drops into BOOTSEL instead of the application when the menu is requested but it fails to load. At least it will make it clearer when something is wrong.
Error messages for UF2s that are bad or for the wrong platform are improved. It will also stay in the menu instead of automatically rebooting, so another option can be selected.
Ejecting and reinserting the SD card while in the menu should now work properly instead of throwing an error and rebooting.