Mac can not read my iPhone 7plus

If you are running 10.6 as your profile shows, your version of iTunes is too out of date to use with the newer IOS versions. You would need to update your OS to Sierra or newer. You would need to update to El Capitan and then update from there.

Check that your computer is compatible with Mountain Lion/Mavericks/Yosemite/El Capitan.

To check the model number hold down the option/alt key, go to the Apple menu and select System Information.

MacBook (Late 2008 Aluminum, or Early 2009 or newer) model number 5.1 or higher

MacBook Pro (Mid/Late 2007 or newer) model number 3.1 or higher

MacBook Air (Late 2008 or newer) model number 2.1 or higher

How to upgrade to macOS Mojave - Apple Support

How to get macOS High Sierra

Sierra download

El Capitan

Check to make sure your applications are compatible. PowerPC applications are no longer supported after 10.6.

Application Compatibility

El Capitan 10.11 Compatibility information

macOS Sierra 10.12: Compatible Apps

Also check to make sure there is a compatible driver for your printer.

Do a backup before installing, preferable 2 backups on 2 different drives.

You are welcome. I'm not sure what you mean by it won't accept updating to a newer version anymore. Have you tried downloading El Capitan using the link I posted above? After reinstalling Snow Leopard, did you do the App Store update? If the App Store is telling you that you need to update your OS to use the App Store, contact iTunes Support.

App Store Update for OS X Snow Leopard

Either use the form or scroll to the bottom of the page in the 2nd link. Follow through the screens to get a chat or telephone option.

iTunes Support

iTunes Support – world wide