@oxfordfam 13.7.8 is the latest for you that OS your HW can take, but OS 13 is out of support as of Nov i.e. your HW is also out of date and Apple won't allow you to upgrade past 13. The latest OS is 26 (now following calendar years so it went 14,15,26 after 13 - see https://support.apple.com/en-us/109033). You'll stop receiving updates from Apple and other third parties like Adobe, MS 365... and Intuit, they don't support Turbotax on unsupported OS versions.
If/when you consider upgrading, Mac minis are a pretty powerful solution you can plug into 3rd party monitors for a flexile setup.
