Arduino core for AVR DA, DB, DD, EA and future DU-series parts - Microchip's latest and greatest AVRs. Library maintainers: Porting help and adviccee is available.
Neither of those options is the one you should be using. The one you should be using is the Reset and UPDI option. That said option is not present is clearly a bug. I didn't name the menu options distinctly.
I belive is what that section of board.txt should be.
#----------------------------------------#
# Reset pin as INPUT, UPDI as I/O #
#________________________________________#
avrddopti.menu.resetupdipinsopti.resetupdi=Reset & UPDI
avrddopti.menu.resetupdipinsopti.resetupdi.bootloader.resetpinbits=11
avrddopti.menu.resetupdipinsopti.inputupdi=Input & UPDI (no reset to enter optiboot)
avrddopti.menu.resetupdipinsopti.inputupdi.bootloader.resetpinbits=10
avrddopti.menu.resetupdipinsopti.resetgpio=Reset & GPIO (HV pulse RST for UPDI)
avrddopti.menu.resetupdipinsopti.resetgpio.bootloader.resetpinbits=01
avrddopti.menu.resetupdipinsopti.inputgpio=Input & GPIO (no reset, HV pulse for UPDI)
avrddopti.menu.resetupdipinsopti.inputgpio.bootloader.resetpinbits=00
From here:
@SpenceKonde mentioned the following.