This seems impossible again for current appstoreconnect. There is no version under General -> App Information. I started uploading several betas (5.6.x) under a major version "5.6", but as it's been many many changes now, I wanted to make it "6.0". There seems to be no way to do that, did try as the OP here to have a version approved for manual release, still did not give me the option to either change, or add a new version.

As with all apps you can only install older versions if you had installed them before. So an older iPhone will get the option to download the previous version, if it that version was installed in the past. Pretty underhanded move, I just found out after adding some new iPhone 6 beta testers :(

This is quite annoying. I had the assets fine from Xcode 13 and thought, hey, why don't I switch to full and add those extra icons? Validation warnings after that :(

Updating to 15.0.1 fixed it for me without doing anything else.

This is still happening. Very bad API behaviour.