Thx, the online sources are not in agreement, possibly because the writers fail
to understand Advaita Vedanta. As to Henotheism, the Wikipedia post has it
right, in that one (like Shankara) can accept the tenet: "Brahman is the world,
the world is Brahman", along with the label "God".
Personally, I prefer the Buddhist perspective in not calling existence (Cf.
MMY's SBAL) "God", even though MMY used the term in one small book. But in the
broadest sense, Shakara's worldview can be called Henotheism
As to the similarity between Shankara's Advaita Vedanta and Spinoza, the
famous linguist Max Mueller was the first to point this out, but the similarity
extends only to what Spinoza called "Substance" (or Being-In-Itself). This is
the same as MMY's "Being", and possibly that of Aristotle, although the latter
wasn't a Monist.
In the West, humanity would have to wait until Plotinus to encounter true
(But alas, no connection to Quietism.)
Spinoza was a further advance, but his approach was through rationalism, and
he also failed to get the connection to Quietism. But a contemporary of his,
George Fox, did get the connection.