Is it true that operations with 8 bit numbers are slower than with 64 bit ones?

Question

C++ / C#

Is it true that on 64-bit machines, arithmetic operations with 8-bit integers are slower than with 64-bit ones, because operations with part of the register require auxiliary operations?

Answer 1

Not true, in a 64-bit register, you can add 8 8-bit numbers at once.

Answer 2

In ARM64 processors - yes.