I just did this to my 2021 a few weeks ago and recently posted an update about it on my IG. From everything I read in the dedicated AC Performance thread, it seems like some early 2021s do have the issue, but most do not. With that info, I decided to try the valve on my truck just to see what difference it made, if any.
With the valve closed, I thought it felt cooler in the cab but the difference wasn't anything drastic like what most 2019 and 2020 owners claim to have. I decided to get average temp readings over the course of the week during the morning and afternoon hours. Both temp tools were providing nearly identical results. I found 3.5-4.0 degrees colder with the valve closed vs open. These results were consistent across the entire week.
Based on the results, I wouldn't think my truck has the dreaded AC performance that the 2019 and 2020s are known for, at the same time, I also found it odd that there was cooling improvement because everything that I read in the forum thread led me to believe that there would not be any temperature differences at all if the the fix was already in place.