How does the committee determine if the reasoning was motivated?

This is a good question. My proposal is entirely theoretical and still in the rough draft stage at this point, and getting any feedback would be of great benefit. I haven't fully worked out how the members of the committee would go about determining if motivated reasoning influenced the decision-making process.

Why not just have the committee make the decision in the first place?

The committee is acting as a check against the decision-making institution, and the ledger system used by the committee acts as an incentive for the decision-making institution to avoid motivated reasoning.

At a guess - there may be a difference in skill/s required to make the really good decisions versus telling if decisions aren't the best, or are "motivated".

Thanks for your feedback. I just want to go over some of your points:

Motivated reasoning plays into most high stakes decisions in big organisations as the decisions matter.

I came up with my proposal as a possible solution to the problem mentioned in the following article: (https://80000hours.org/problem-profiles/improving-institutional-decision-making/). I guess I should have mentioned this article in my proposal.

when you give a lot of political power to your "checks and balance"-committee that's going to act politically as well and won't just follow norms of abstract reasoning.

I mentioned in my proposal that the members of the committee are supposed to be non-partisan, so the members of the committee are not politically motivated. I didn't mention anything in my proposal about the checks and balances committee being regulated, and that is a modification that I should make.