You probably have to bite the bullet at some point, since Microsoft has stopped supporting Office 2011 years ago.
So that means either upgrading to Office 365 sub or single purchase of Office. Or look at a different suite like Libre Office. Last one is free and pretty good with handling Office files. It's not perfect though, so you might want to toy around with it to see how well it handles your files.
I've went with an Office 365 sub years ago. So I can run Office on both my MacBook Air and my Windows 10 laptop. The 10 euro per month is the same that I would pay for the 1 tb OneDrive storage that comes with Office. So for me it's basically using Office for free :)
Do I use iCloud for storage? Well I do have an Apple One subscription so I do have 50 gb storage there. But that only gets used for my Mac's needs. My personal files are all on OneDrive :)
Good luck :)