MS Word is not our word processor of choice, yet it comes with the MSO 2021/365 package and is automatically installed.

Is there a way to either uninstall only MS Word or prevent MS Word from running on a PC?

Yes, uninstall Office. Beginning with Office 2013, Versions of Office have been all or nothing installs. You can also purchase individual applications and pay a lot more.

If you have another program that you want to be using for word processing and handling .docx files, tell Windows that you want to open .docx files using that program. Then, when you double-click on those files, they should open in your preferred program.

Thanks for the reply, but on this MSO 2021 & 365, I've only seen the options where it does a full install of all the available programs, and I've must've installed MSO 2021 & 365 on at least five different PCs, and have never seen the prompt to only install certain programs, e.g. Excel, Outlook & PowerPoint.

There is no such prompt. Beginning with Office 2013 it is all or nothing.
You can buy individual applications like Outlook, PowerPoint, Access, Word or Excel but the price is high at about $160.00, each. (Each has a non-commercial use version available for about $80.00.)

This is different from purchasing the suite of products which are bundled, again, all or nothing. There are different bundles, but all include Word.

Again, even with Word installed, you are not forced to use it.

I'm not sure which other word processor is your choice, but you could probably set your default programs for various file types (.doc, .docx, .txt, etc.) to your other program, and remove the shortcuts to Word. That's presuming those file types are 100% compatible in your preferred application.