MacOS 10.16 Big Sur needs to be updated please send me a link. Thx

Select the Apple () menu > About This Mac and from that panel, compare what is in parenthesis to macOS Big Sur is compatible with these computers - Apple Support. If that is satisfied, then visit How to download macOS - Apple Support with the Safari browser and download the full Big Sur installer to your /Applications folder.

Before you apply any upgrade from Catalina, confirm with any third-party application, printer and scanner vendors that they provide current software and drivers for Big Sur.

Perform a last Time Machine backup of your iMac before any upgrade.

Big Sur is currently at v11.7.3.

That 2012 iMac cannot upgrade to Big Sur and unless you are prepared to purchase (or borrow) a newer Mac (or PC) that meets the installation requirements for Turbox Tax 2022/2023, you are done, short of doing your taxes manually, or paying a tax service.