Function vcopyq_lane_u16 

pub fn vcopyq_lane_u16(
    a: uint16x8_t,
    const LANE1: i32,
    b: uint16x4_t,
    const LANE2: i32,
) -> uint16x8_t

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

Insert vector element from another vector element Arm’s documentation