Technically, on ARM, you can chose what endian mode you wish to use, you can even chose between two big-endian modes on many of them.
Indeed, but this feature is not mandatory. Many embedded market ARM chips are Little Endian only without option to switch endianess. Most high power class CPUs are though still bi-endian. My Emu68 runs actually in 64bit big-endian mode on RasPi machines as well as on RK3399 CPUs.