Please keep this forum in English.
I would assume you are referring to mod config guis, which only work if you are using Forge version 1.14.4-28.1.56 or later with a mod that has a config gui.
Since both blocks and therefore item blocks have 3D models and items can also be 3D; it would make more since for your buttons to hold an ItemStack and then render the ItemStack on top of the button.
This solved the problem for me
First register your entity with custom client factory like this
.setCustomClientFactory((spawnEntity, world) -> new ExempleEntity(world))
And then use NetworkHooks#getEntitySpawningPacket to get Entity Spawning Packet
@Override
public IPacket<?> createSpawnPacket() {
return NetworkHooks.getEntitySpawningPacket(this);
}
that's it ?