R’ Avinoam continues:

To summarize and connect some of the points in SE. צמצום has the same gematria as יקוק + ספק. This is a key concept. If no Tzimtzum, then there is absolute certainty/knowledge. With absolute certainty there is no free choice. The more Tzimtzum, the more uncertainty, the more free choice. Free choice is simply a function of Tzimtzum.

According to the Leshem, if Adam HaRishon were to have been fully in Atzilut when he was created, he would never have sinned. It was only because his lowest levels entered the 6 highest Sefirot of Beriya that he was capable - i.e. had the free choice - to sin. This means that even at his incredibly high level, he had an element of free choice - and he chose.

Another crucial point about this is that Tzimtzum is only from OUR perspective - מצדנו. Therefore free choice is only ever from OUR perspective. Therefore מצדו there is no free choice - and everything right down to the most minutest detail plays out, at every world/level of existence, according to the Divine plan. It is only free choice from our perspective - and at the same time, from our perspective it is very real and we genuinely have the choice to perform Mitzvot (and this is the same as saying that the Torah, which is manifest in the language of our perspective is also very real from our perspective).

So, where is free choice. It resides in the fabric our our existence resulting from Tzimtzum. It is mine and yours and makes us accountable because we are each a חלק אלוק ממעל ממש wrapped up in a Tzimtzum existence and that חלק אלוה (or perhaps more accurately חלק יקוק) is exposed to ספק and that is the very essence of free will.

Hope this is clear and satisfying.

(The discussion about Tzimtzum and Safek is before and after SE, p. 802.)