There's also rav1e (rust AV1 encoder) which has a heck of a lot of ARM64 SIMD optimisations due to porting them over from dav1d.The x265 library is currently lacking ARM SIMD optimizations. So you better use the X264 library, which is relatively good optimized for ARM64 or wait until X265 is also optimized - it is currently being worked on.
Making it currently better provisioned for 10 bit SIMD than all x86 SIMD platforms currently.
Conversely to x265, dav1d/rav1e has no 10 bit SIMD for x86 platforms and most of the ARM64 SIMD is done I think.
On 8 bit content it should be fine for making comparisons though, both ARM64 and x86 SIMD are pretty matched for completeness.