Unable to update bootloader on 4630

Hello @lysander
Did you upgrade your bootloader? => Bootlaoder update

When you push the reset button twice quickly, does the RAK4631 show up as an UF2 drive in Windows?

This part of the error message points towards a problem with the COM port being occupied:
I made the bad experience that Ultimaker Cura (3D printing software) is occupying all COM ports it finds (hoping a 3D printer is attached somewhere) while it is running. Make sure nothing else that uses COM ports is running.