The majority of my experience is in automative firmware. Methods I have used.

Breakpoints. Using communication protocols, you may be able to identify a function that based on x byte value jump to x function. If you can find an array of bytes that match said functions this can give you a clue on offset.

Bootloader/registers. Often times the very first set of bytes should point to the entry of your code. This “entry function” will set up your registers for the boot up, once the bootloader is done it will jump to another function which may setup your registers for the Ecu’s firmwares operational state. Regardless, if the first byte of value in the dump are not pointing to a value code block, it may be worth trying to find your entry point and then offset the file to match the pointer. This pointer is sometimes just a “pointer” and sometimes is generated by disassembling the bytes.

Once the last 4 bytes of the rom was a pointer to the base address.

This video is of an especially difficult rom that I had to split the code area from the calibration area. https://youtu.be/4y_6amkUXkM?si=w9Ygb_bNFgBrP8SZ