Minecraft maps render themselves and the player's hand when are hold. You can check PlayerRenderer class and look for renderRightHand or renderLeftHand methods, and provide compatibility for other mods that do the same thing. (I used neoforged 1.21.1)

What exactly do you mean by that? You can't see the armor when you use your arms to see the map?

I will close this issue because the problem of the armor not being rendered when using the 2 hands map has been solved, thanks for the report.