You question: If "you are not the doer," as the nondual sages say, does that mean that we are simply subject to fate?

Fate is defined as "the inevitable outcome of events, as predetermined by a superhuman agency, or god."

We have been enculturated, for centuries, with the notion of a celestial agent (or agents, before ancient religious currents reduced it to the singular) directing the affairs of humankind and worldly events so that these are pre-determined. There is a dualistic premise to this conception.

As early as the Hebrew bible (so-called Old Testament), the first verses of Genesis ("God created...") depict God hovering over—thus distanced from—the earth. His persistent activity, from thereon, is to separate this element from that element (light from darkness, ocean from land, etc.—beginning with the "formless and empty.")

Even into the New Testament, centuries later, this agent, positioned in a heaven, was described as acting upon—fatefully—the person of His own surrogate, Jesus.

The point of view of the nondual teachings is that there is not a god which exists "hovering over" the world and man.

Nor was the "world created" by such a personalized figure (Gen. 3:8, "walking in the Garden in the cool of the day"!), in the past tense.

That which is creating (and destroying) is present at every point in space and time: it is what is being created and destroyed. It need follow no particular preordained outcome, because—being unopposed by programmatic limitation—there isn't any outcome which can be wrong.

In other words, this Absolute presence is what is being done—in, by and as everything which exists (or doesn't exist). It would therefore be anything which could be predetermined, as well as anything which was not predetermined; the fated outcome and that outcome which was not fated. So, fate really has no relevance in such a context.

Even those who are relatively spiritually sophisticated have difficulty recognizing their conditioning which predicates a remote and willful instigator of particularized outcomes.