Unloaded Crossbows can't be equipped by Armour Stands, in survival without any arrows, it does nothing. But if you have any arrows in your inventory or you are in creative mode, it has a loading animation that only shows less than half seconds. But it works perfectly fine with Loaded Crossbows.

I am using Oppo A71k

Steps to Reproduce:

1. Spawn or Place an Armour Stand.
2. Obtain Unloaded Crossbows and press the Equip button or right click to the Armour Stand you have spawned.