The universe is just one enormous 'Soul Filtering machine'

[Angrboda]

If they do not sin because of "the way they are" then you are no longer arguing that they have free will but rather that their behavior is in some sense determined.  You've undermined your argument for one.  For two, your answer is so vague that it basically reduces to "they would not sin for some unspecified reason."  That's hardly adequate as an explanation for why they would not sin.  It's little more than a bare assertion of your conclusion.  Christians have said that we are "slaves to sin."  Even those who accept Jesus as Lord and Savior continue to sin.  That is "the way they are." You need to do more than just handwave at some unspecified reason to explain why they will sin no more once in heaven.

I was not getting into why they did not sin--only countering an argument that God could create people in a "dimension" where they would not have chosen sin.
There are several possibilities. The doctrine of Sanctification is where a Christian is perfected in love, meaning that the heart is undivided in its love for God or that it loves nothing that conflicts with its love for God. It is reasonable to assume that being in the actual presence of God (or having access to the actual presence of God) has the effect of preventing a divided heart.

It didn't stop the Morning Star from having a divided heart. What makes you think it will for the average human.

In addition, whatever additional knowledge (promised in scattered versed throughout the NT) becomes known to us in heaven would likely have the effect of illuminating the consequence of sin and therefore eliminating the desire for it. Anyway, there are no logical problems with free will existing in heaven.

Knowledge has never been a palliative for sin. And why couldn't God create these beings already imbued with this knowledge, or for that matter already in the presence of God. Neither explanation offers a reason why God could not create beings who do not sin without going through the test. Both can be applied at creation, if indeed they are the reason people in heaven do not sin.