Great! So please explain what algorithms are used by these "nonpartisan" commissions?

I’ll reply in good faith even though I detect sarcasm in your comment.

Generally nonpartisan commissions prioritise contiguity and compactness. There is an element of “I know it when I see it” because you’re trying to avoid both packing (packing minority voters from disparate areas into one) and cracking (distributing a minority district like Salt Like City into its 4 neighbouring districts, ensuring the city can’t vote for … whoever cities generally vote for).

So there is a human element involved, but these commissions generally do a reasonable job. You know how we know? States that move from nonpartisan to partisan commissions cause a dramatic change in the results of the next election. If the nonpartisan was biased like you imply with your air quotes, we wouldn’t observe that effect.

Also there are algorithms to draw fair districts without needing human judgement. See this paper[1] that expounds on one such algorithm.

1 - Swamy, R., King, D. M., & Jacobson, S. H. (2022). Multiobjective optimization for politically fair districting: A scalable multilevel approach. Operations Research, 71(2), 536–562. https://doi.org/10.1287/opre.2022.2311

They're not.