Updating an older iMac

That model can not be upgraded further.

One thought is to try Turbo Tax's online filing, that may work for you. Otherwise it's time to upgrade to a newer iMac. If money is an issue then consider an Apple refurbished iMac. They have no downside at all! They are identical to a new iMac, come with the same 1 years warranty, are eligible for AppleCare, typically are current models and can save hundreds of dollars. The downside is the sell FAST! Inventory changes quickly so when you find the model you want then be ready to buy. Also, if you have good credit they are eligible for Apple's financing. You can find them under the Refurbished and Clearance section which is at the bottom of Apple's home page, www.apple.com.

Good luck

That is the one deal-breaker, mission-critical software that I use every year that basically is my personal deciding factor for when I have to get a new Mac. I prefer to use the .app on my computer, either the physical CD or download option. (my 2010 Mac is OS limited to 10.13 and not supported by Mojave, so I am going to be looking to upgrade soon myself).

An alternative to the .app version that you run locally on your machine, they do have an on-line version which expands support to older hardware/software versions, all the way back to 10.6 Snow Leopard which you access via a web-browser.

https://ttlc.intuit.com/questions/1899861-turbotax-online-system-requirements

"Mac OS X 10.11.x (El Capitan)

• Firefox 40.x
• Safari 9.x
• Chrome 40.x
• Opera 36.x"