Hello. I found another completed project A during the app development test. I pasted only the extension file added from project A to project B in finder. However, there was a problem with info, so it was impossible to build. I deleted it and tried to build it, and it worked very well. However, when I rebooted my development system mac and re-run the project, there is only the extension and the app product is not selected for build.
The first problem that occurred here is I don't understand why the build works if I delete info when another extension is copied to finder. And for the second problem, I don't know why only the extension appears and it is impossible to build the app when I run xcode again. I would be grateful if you could leave a guess, even if it is not an exact answer.