Opening the Curios Inventory removes the Inventory Button.

I opened a issue at Curios github
TheIllusiveC4/Curios#47 (comment)
and they said they cannot fix it and the button has to be added to their inventory as well.

Is this a problem tho?
It only happens when open the Curios inventory, do people uses Curios inventory as main inventory or something?

Yes. The key idea is to open Curios Inventory with "E" instead of the normal inventory.
Because I don't see a reason why you would want to close Curios except for the reason mentioned in this issue.