Is it just me or Apple Developer forum is so empty? I just started doing development for MacOS and so far it seems like the forum isn't such a great place to find answers.

This is the correct solution for me. I changed mine to "Mac Developer" since my app is only built for macOS. I was trying to integrate Sparkle to do automatic updating on my app but kept running into the same error the OP has here. I even checked that the framework exists in my build according to this post: https://developer.apple.com/forums/thread/705728). For anyone else trying to figure out where the Code Signing Identity is, it's under Targets -> Build Settings -> Code Signing Identity