Arelith

Invoker is not a part of any of the required classes for any of the rituals, perhaps intentionally, or perhaps they simply haven't been added to the lists. Hopefully They get added to them at some point, along with a few items in game that all other arcane casters have access to.

They are not actually linked to any in game mechanism other than scrolls/wand use as an arcane user right now.

Meaning:
No Rituals
No Craftables
No Arcane Tower “special store” access
Not even a defined ioun stone for them to use