Our clients require us to use Microsoft apps. We also like to collaborate on docs and excels in Word-For-Web. But to open Microsoft files from a dropbox finder window, it's a three click process to open in word-for-web for collaboration:
Right click>quick-actions>open on dropbox.com
Then: Open in>word-for-web
There should be a right-click quick-action to open a Microsoft document directly in Word-for-Web.