The iTunes app may be gone, but you can still back up your iOS device to your Mac.

For iPhone and iPad users who still connect their devices to a Mac for syncing and backups (and there are a lot of people who still do this), there are changes coming in the next version of the Mac operating system. In macOS 10.15 Catalina, the iTunes app is gone.

Now you use the Finder, similar to how you see a hard drive or a server. Here’s how to use your device in the Finder and how to back it up.
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https://www.macworld.com/article/3410567/how-you-back-up-your-iphone-and-ipad-in-macos-10-15-catalina.html