thanks. I have checked already the help files provided within Xcode's top-menu-bar "Help", which includes the Xcode-support site. And google. And all available settings under Xcode's top-menu-bar "Settings". And within Xcode's top-menu-bar "File -> Project Settings". And every option available under each of the Xcode's top-menu-bar sub-menus. For completeness I just searched "jump bar" within the top 2 links that you provided. I don't find anything that is related to the jump bar settings. This is java code that I'm working with, if that helps.
One possibility is that it is an obscure option within some plist for Xcode that is not well documented, although I don't know how it got set that way for this computer while not for my other computer that I use when looking at the same Xcode project files. My other computer has identical hardware, same Mac OS, same version of Xcode.