I'm having the same problem, has anyone figured out what should be done? I tried to ask the review team but no reply.

Correct, my wording is bad there. I'm not trying to connect it to my build. But I select a build, and then there should also be an option to attach the IAP to the new distribution in App Store Connect, but it isn't there. I have seen it once before, and I have attached an IAP, but that app version was rejected and the IAP was returned and now my current version was approved, but my IAP is rejected and they want me to add it, but the option isn't there to do so.