First thing first: when I speak about open decorators I mostly refer to the
delegate_all (anti)pattern introduced in many Rails applications by the widely used draper gem.
With "open" adjective I refer to the fact that the decorator responds to all the messages as the underlying decorated object. This is like a transparent ill variation of the proxy pattern: if you need proxy pattern[^1] then you want to re-bound the interface, lowering required knowledge as much as you can, lowering responsibilities and lowering the maintenance of boundaries between objects and application layers as much as you are able to.
While the family of decoration patterns[^2] is large and with subtle differences between one member and another, I consider Draper's decorators as decorators for the view layer, thus we could speak more of a presenter[^3]. The readme of the gem itself says