Google is telling me, along with some of my banking websites, that I need a newer version of MacOS. My model is late 2013 21.5 inch. When I go to the look for updates, none show in the App Store. Can I still upgrade to Mojave or Catalina like the articles I've read state?
iMac 21.5″, macOS 10.13
To upgrade the macOS, see > Update macOS on Mac - Apple Support
If that doesn't work? Then you may have some type of third party AV, Protection, Cleaning software or a VPN that is blocking your iMac ability to update and/or upgrade.
To override third party software try starting up in Safe Mode and the Upgrade.
see > If an error occurred while updating or installing macOS - Apple Support
Your iMac can upgrade to Catalina. You'll need at least 12.5 GB of free storage to upgrade.
You can download and install Catalina here: https://apps.apple.com/us/app/macos-catalina/id1466841314?mt=12
iMac needs to be upgraded from High Sierra
