You can still use the spear in spectator mode

Take a Spear in your main hand, switch yourself to spectator mode, and then use the left click; you can still hear the sound of the spear. If you quickly switch to another mode, you can also see the spear thrusting animation.Even though you can't cause any harm

Under normal circumstances, no matter what you hold in your main hand, you cannot use it in spectator mode. However, when you have a spear in your main hand, you can still use it, hear sounds, and even play animations, which is incorrect.