For me it works as expected. The ROM update reboots the Amiga and you have to change the boot options after each reboot. So you have to wait until the ROM update is active and only then hold down both mouse buttons. You can see that the ROM update is active by the fact that the new options Double PAL and Double NTSC are available in the Display Options of the boot menu.
This. I had the same issue switching from NTSC mode to PAL mode, gotta wait for the second boot to change the options.
