Hey, it looks like I've partially sorted out the issue. I was using this command before:

idf.py flash

It worked fine when Secure Boot was disabled in menuconfig, but threw an "invalid magic byte" error when Secure Boot was enabled.
Here's what I'd see in the console while flashing, if it helps ...

Hi, and thank you for your response.
I did read the documentation you provided. My apologies if I didn't make that clear initially

Here's my workflow:

Creating the project
idf.py create-project secureboot_test
cd secureboot_test

Writing some sample hello world code
nano ./main/secureboot_test ...

Hello. I have an ESP-WROOM-32 ESP32 I'm trying to enable Secure Boot v2 on.

I've gone through menuconfig and selected "Enable secure boot version 2"
When I try to flash I get an error saying the bootloader is too large:

[100/101] cmd.exe /C "cd /D D:\Dev\esp-idf\hello_world\build\bootloader\esp ...