Cannot install Microsoft 365 on 21-inch late 2013 iMac

janefromsurrey wrote:

Can't install Microsoft 365 on my 21 inch late 2013 iMac.

Microsoft only allows new installations on Macs that are running one of the three most recent versions of macOS. Catalina fell off that list many years ago.

I'm running Mac OS Catalina 10.15.8 and I think I need more updated current software..

Your Mac is too old to run anything later than Catalina.

You could consider replacing it with a machine like a 24" M4 iMac, a M4 Mac mini, or a M4 Pro Mac mini. (You'll need a standalone monitor if you get a Mac mini. It can be, but doesn't have to be, an Apple-brand one.)

If you want to try sticking it out with the old machine a bit longer, Catalina is enough to run

• The current version of the Firefox Web browser
• An archived, unsupported version of the LibreOffice office suite. According to The Document Foundation Wiki – Documentation/System Requirements, version 25.8.x.x is the latest one compatible with Catalina. It looks like the latest version is 25.8.7.3 – you would want to go into the "mac" folder and then into the "x86_64" one.
• The parts of Affinity Studio that are "free with registration". (The AI stuff requires a subscription and a much newer Mac.)

No. macOS Catalina is as far as that iMac can update. It's at the end of update support.

Current Microsoft Office 365 apps from the Apple App Store app require macOS 14 Sonoma not 12 Monterey.

If you have an older Microsoft Office installer it may work on Catalina, but Microsoft was disabled the activation servers for older Office versions.

You may still be able to activation Microsoft Office 2016 and 2019 on Catalina if you have a valid Key.