What is the newest macOS that will run on my mid 2010 iMac (21.5")?

What is the latest macOS that will run on my mid 2010 iMac? I am currently running High Sierra v10.13.6 but I downloaded TurboTax 2020 and it says it won't run on the current iOS and I need to upgrade to a newer version macOS to run TurboTax 2020. I don't know if that means Mojave, Catalina, or Big Sur since it doesn't say? If I have to upgrade computers to get a newer macOS to run TurboTax, I'm not going to be very happy since the mid-2010 iMac still works fine otherwise.