Immersive Engineering Outfitter villagers need a banner which has been right clicked with a shader as their workstation(shader banners), but those can only exist in world and not inside trader blocks since shader banners drop regular banners when broken.
Possible solutions that would work for other non item based workstations could be some way to link trader blocks to workstations in-world, or the ability for a trader block to consume a block near/on top of it for its workstation. Currently no other villager types use blocks that can't be picked up as workstations in mods that I know of, but there is the possibility for there to be more like this, such as a villager type that uses an unbreakable block as its workstation, so this would futureproof things a bit. Alternatively could just add some IE compat by allowing banners to be put in traders and then right clicked with shaders like normal but that might be harder.

I'm sorry, but I think there is no simple solution for this problem. Maybe ask the Immersive Engineering devs, if they could change the block for one that is breakable.
But if they want to have their workstations not movable for a reason, then I can't do anything about it.
I won't change the core mechanics for a mod with a strange villager workstation mechanic.