The very simplest bootloader example. Boots directly into bootloader, then loads a blinky example.
You'll need the rust embedded toolchain: https://docs.rust-embedded.org/book/intro/install.html
The point here is that the booloader sits in the start of the flash memory address space:
// bootloader/memory.x
FLASH : ORIGIN = 0x08000000, LENGTH = 32K
The blblinky example code starts two pages later:
// blblinky/memory.x
FLASH : ORIGIN = 0x08008000, LENGTH = 96K
In total, 128K of flash memory can be used (32K for bootloader, 96K for user application), your MCU might have more memory.
The bootloader code (main.rs), does nothing more than executing the code starting at memory address 0x08008000, but you can now adjust it to your liking.
You need to flash both projects successively to run the code, the order doesn't really matter. Use cargo flash if possible and make sure the whole chip is not erased when uploading the binaries (should not be set be default).
It would be good to showcase a method to write binary code to the flash memory to do OTA updates. For an extensive example see here: https://github.com/karthickai/rustboot
See the bootloader and blblink folders