iMac and desktop using same Word licence

My wife is using my desktop for some work from home. She uses Word, Excel etc and I have the same software installed on my 27" iMac.

So far everything has went fine until I was using a spreadsheet of my own this morning and the following message appeared on the spreadsheet. " Action Required We've detected a one-time purchase licence. This licence can only be used with Microsoft 365 apps downloaded directly from Microsoft365.com".

I now suspect that I will have to purchase a separate licence from Microsoft to re install on my iMac to keep using Office for my own work. The desktop still seems to be working ok when I recently opened a spreadsheet. Don't have a problem with buying a licence but can anyone give me a steer how I should do it? For instance should I buy a new separate licence for the laptop and install it on that pc and then go back to using Office on my 27' as normal?

I will probably buy the new software from Apple Store as I am somewhat supicious of some online vendors and my experience leads to lean towards Apple.

I am not keen on a one year subscription payments.

Any help would be appreciated