HOW DO I UPDATE MY MAC FOR IOS 14, CAN'T USE TURBO TAX WITHOUT IT

iOS is for iPhones and iPods not Macs. iOS 14 is for iPhones and iPods.

Macs Run macOS. The current macOS version is macOS 11 Big Sur. Prior to that, is macOS 10.15 Catalina.

The online version of TurboTax is supported on Macs running anything from 10.9 Mavericks to the current macOS 11 Big Sur.

https://turbotax.intuit.com/personal-taxes/online/system-requirements

The desktop version of TurboTax does require 10.14 Mojave, 10.15 Catalina or 11 Mojave.

https://ttlc.intuit.com/community/system-requirements/help/minimum-system-requirements-for-turbotax-mac-software/00/25609

What you can update to, will depend on your exact Model / Year of Mac.

A late-2012 to 2014 iMac can be upgraded to Catalina 10.15.7 -- see: How to get old versions of macOS - Apple Support

A 2014 or later iMac can be upgraded to Big Sur. See: How to upgrade to macOS Big Sur - Apple Support

The model year of your iMac is shown in Apple menu > About this Mac.

If your iMac is before the late-2012 model, you can use the online version of TurboTax. I have a 2020 model MacBook Pro and I use the online version of TurboTax. It will run on much older systems. See: https://turbotax.intuit.com/personal-taxes/online/system-requirements