if I click update, will it only update the software for the itunes and phone or will it update with catalina?

Trying to back up an iphone and get the window that I need to upgrade software. if I click update, will it only update the software for the itunes and phone or will it update with Catalina? I have been avoiding that update since I need to use Bento for a club database. If I update it will no longer be compatible with this computer . This computer is old, early 2013 lap top w/ retina display, and the sound is gone. Sound will not even work with blue tooth speakers or connected. So decided to leave this computer to use Bento. I do want to back up my IPhone though.