Modern-ish CPUs have instructions to load big-endian data without having to switch into a special 'big-endian mode', and compilers can optimize into those instructions so language don't need to add special intrinsics:
https://www.godbolt.org/z/q3hMPq78v
...but even without specialized instructions the transformation should be pretty much free on pipelined CPUs (compared to a memory load anyway).
It's still one more thing you need to keep in mind when writing code, at least in languages that don't have a separate data type for different-endian fields.