The text manipulation and editing in the Song Editor and other places in OnSong is handled by Apple's operating system. Newer versions of iOS/iPadOS may change how you interact with text. You can learn more about the new copy/paste gestures in this article.
Some users experience issues with text handling after installing iOS/iPadOS updates. You may want to try restarting your device to see if that clears up the text menu issue, as again, this is handled by Apple's operating system and not by OnSong directly.