(IFF) all events are CAUSED (THEN) determinism makes your decisions (not "you")

No, free will means that our decisions are in fact caused, but by us. We are causal agents, we are the cause of the things we do, and since our actions are caused by us, the only thing that determines our decisions is ourselves.

Well, "simultaneous causality" is also incompatible with "freewill".

No, because in that case it cannot be traced back to antecedent causes to our will. Our will would be the cause of our decisions, and we cannot go back to past events to explain our will.

In order to "solve" the "freewill" question we don't need to know "the origin of the initial singularity" (which is beyond our epistemological limits).

If we start from the premises you have given, namely, that there is an unbreakable chain of causes and effects, in a linear view of time, and in which causes always precede effects, then it is inevitable to ask ourselves about the original cause of everything, and in that case, it would not be beyond our epistemological limits because it would be a necessary consequence of what we already know.

It is only necessary to realize that the first cause of all could not be caused by another antecedent cause to understand that determinism itself is contradictory. And, again, this does not escape what we can know, because it is a necessary consequence of its own premises.

(IFF) SOME events are CAUSED and some are UNCAUSED

In my opinion, it is not that there are events that are uncaused and events that are caused, all events must necessarily be caused, but the causes of those events are not caused, because if they were caused, they would cease to be causes and would become effects. Causes should be, by definition, uncaused, and it is a great mistake, in my opinion, to speak of causes as if they were effects.

All motives (goals) that drive your "decision making" are caused by previous events.

And the only "alternative" is that some of your motives (goals) are "uncaused" (making them indistinguishable from random).

The motives are not caused by past events, but by present conditions, if I am thirsty and want water, I do so because in the present my body is dehydrated, not because I have not drunk water in hours. In any case, that I have motives to do something does not mean that I am going to do it, I may be thirsty and decide not to drink water, therefore, although my motives may be caused by external circumstances, not my decision, which is influenced but not determined.