When using Zephyr, it is common to use mcuboot as the bootloader. However, you sometimes need to configure mcuboot separately from Zephyr. In order to do this, use:

west build -t guiconfig --sysbuild --domain mcuboot

The thing to remember here is that when we are doing a sysbuild(which is needed to build both the bootloader and your code), you can’t just do a normal guiconfig as this will configure your application, not mcuboot. So you need to tell the build that you want to configure the mcuboot domain.

I keep forgetting this, so putting it down here for future reference!