Consider variable-length integers for file sizes and string lengths. When I need them, I usually implementing what’s written in MKV spec: https://www.rfc-editor.org/rfc/rfc8794.html#name-variable-si...

That’s a good way to bypass that 4GB size limit, and instead of wasting 8 bytes per number this will even save a few bytes.

However, I’m not sure how easy it is to implement in the language you’re using. I only did that in C++ and modern C#. They both have intrinsics to emit BSWAP instruction (or an ARM equivalent) to flip byte order of an integer, helps with performance of that code.