Function vcopyq_lane_s8 

pub fn vcopyq_lane_s8(
    a: int8x16_t,
    const LANE1: i32,
    b: int8x8_t,
    const LANE2: i32,
) -> int8x16_t

Available on target feature neon and (AArch64 or ARM64EC) only.

Insert vector element from another vector element Arm’s documentation