Function vcopyq_lane_p64 

pub fn vcopyq_lane_p64(
    a: poly64x2_t,
    const LANE1: i32,
    b: poly64x1_t,
    const LANE2: i32,
) -> poly64x2_t

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

Insert vector element from another vector element Arm’s documentation