SVE and SVE2 do not define the size of the vector registers, but limit the range, from a minimum of 128 bits up to a maximum of 2048 in 128-bit wide units.
Complete the sentence: the size of the predicate register is...
SVE is vector-length agnostic and a predicate-centric architecture with vector registers and predicate registers. Predicate registers are 1/8th the size of SVE registers (1 bit/byte).
Not all Arm v8-A processors support SVE instructions. However, they can still run SVE applications using the Arm Instruction Emulator. Armv9-A builds on SVE with the SVE2 extension.