Actually don't worry! I think it's some fancy things Qt's deployment tool's doing.. I could go look at the source code for a better solution, but I'll just work around it for now. I was trying to copy the Plugins from my local Qt install, which didn't work, but copying from the build that's been through Qt's deployment tool worked. For now I'll just manually coping things over.. Thanks so much for your support @eskimo! Couldn't have gotten here without you!

Yes!! Finally! I managed to get it through to App Store Connect! :D So I removed the call to Qt's deployment tool, macdeployqt. Instead, I tried to do what it does without it, namely copying the Frameworks, Plugins and Resources. I used Xcode's embed and sign Frameworks feature and Copy Bundle Resources to cover the Frameworks and Resources. I tried to use a Copy Files step in Build Phases to copy the Plugins, but it'd give me build errors saying failing to sign no matter if I tick the Code Sign box. For now I got around it by manually copying the plugins from another bundle that I deployed with Qt's deployment tool... Then Xcode's organiser manages to re-sign and upload! Still a bit hacky but at least I got there! Any advice on what I'm doing wrong with the Plugins?

Thanks for explaining the Xcode signing workflow! That makes sense. Yeah true, I agree about these “hard-to-debug code signing and distribution problems”..and that they may show up only on the user's machines. I'll have a deeper look into the bundle structure and figure it out! Thanks so much for your help!! 🙏

Thanks for your reply The Eskimo! It helps a lot to know that it's done before by others! :) Thanks for the pointers! I will look into these directions! Another question, when I use the Automatically manage signing feature in XCode (15.0.1), it only gives me the option to select a Development Signing Certificate. I saw some people online saying we were meant to just use the Development certificate with Automatically manage signing, even for distribution. Should I uncheck Automatic signing and select the Distribution certificate? Or is there a way I can make the Distribution certificate show up?

I'm not sure if it's actually possible to publish a Qt app in the Mac App Store..please advice if anyone has done it!