Function vcopy_laneq_p16 

pub fn vcopy_laneq_p16(
    a: poly16x4_t,
    const LANE1: i32,
    b: poly16x8_t,
    const LANE2: i32,
) -> poly16x4_t

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

Insert vector element from another vector element Arm’s documentation