Make sure arm-none-eabi-gcc -v shows version properly (add bin folder of the toolchain to path environment variable if not. In my case that path would be C:\Program Files (x86)\Arm GNU Toolchain arm-none-eabi\11.2 2022.02\bin)
To bootload program onto OpenMote (here showing openwsn-fw/projects/common/bsp_radio_tx): scons board=openmote-b-24ghz toolchain=armgcc bootload=<OPENMOTE_PORT> bsp_radio_tx
Two ports will show up for the OpenMote. Use the one with the higher number in the command above.
On Windows I experienced ERROR: Timeout waiting for ACK/NACK after 'Synch (0x55 0x55)' . This was resolved by going into device manager and locating the COM ports for both devices and changing the baud rates to 115200 for both COM ports associated with the OpenMote