Can't run Startup Security Utility via Recovery Mode on Mac Studio

I have a new Mac Studio. As part of the process of setting it up I used the Startup Security Utility to temporarily downgrade the boot sequence from "Full Security" to "Medium Security" to enable some system extensions from OWC's SoftRaid app. This worked OK and my raid drives are now operating normally.

I now want to return the boot sequence to "Full Security" but for some reason I can't get the Mac Studio to access the Startup Security Utility when it starts up. What should happen is when the Apple logo is displayed during the boot sequence Command-R enters the macOS recovery mode and you should be able to select the Startup Security Utility. However, this doesn't work for me. I don't see the Apple logo, it just jumps straight to the login page for my user account. I've tried holding Command-R from the moment the Mac Studio starts, tried doing the same from a re-start. I've tried doing this with my Magic Keyboard connected via Bluetooth and connected via USB. Nothing seems to get Mac to enter the Recovery Mode.

Am I missing an obvious step? One of the disadvantages of not have the Full Security setting at startup is that I'm unable to use Apple Pay, so I'd like to get this fixed asap. Grateful for any advice received.