Greetings @jonk4m,
It’s actually not necessary to rebuild TorizonCore to get into the initramfs shell. Instead you can do the following in U-Boot:
Run the following commands in the U-Boot prompt to get a shell in initramfs:
setenv tdxargs plymouth.debug shell
boot
An alternative is setting the ramdisk init application:
setenv tdxargs rdinit=/bin/sh
boot
Either method should drop you inside the initramfs shell to poke around.
Best Regards,
Jeremias