I needed to create a new distribution certificate to upload my app to test flight. to do this, I created a certificate request via the keychain access tool. I then went to the Apple developer portal and created a distribution certificate by uploading that request. I then downloaded the certificate and added it to the keychain. When I attempt to upload, I get the missing key message:
"[name] has one Apple Distribution Certificate but its private key is not installed..."
How is this possible if I am on the computer that generated the request?
Upgrading xCode fixed the problem. I was on 11.3.x and upgrading to 12.5 completely fixed the issue. I then ran into app bundle id issues (which were easy to fix), which makes me think perhaps xCode was just giving me the wrong error message. Regardless, upgrading fixed the problem.