Office 2016 on my 2010 MBA regularly prompts me to update the software, except the updates require an OS upgrade and I'm quite happy with Catalina - besides, the hardware almost certainly wouldn't cope with the requirements of later releases.
I've become irritated with the banner prompting me to install unattainable updates and found this guide on how to permanently remove it.
Having located the folder containing the AutoUpdate program that phones home to Redmond, I deleted it from the computer.
After that, I reopened Word and the bothersome banner is no more.
Nice and easy. If you're also experiencing this annoyance, you can follow suit and get rid of it.

I've become irritated with the banner prompting me to install unattainable updates and found this guide on how to permanently remove it.

Having located the folder containing the AutoUpdate program that phones home to Redmond, I deleted it from the computer.

After that, I reopened Word and the bothersome banner is no more.

Nice and easy. If you're also experiencing this annoyance, you can follow suit and get rid of it.