A family of Microsoft word processing software products for creating web, email, and print documents.
Hi!
Welcome to the Microsoft Q&A forum.
Unfortunately, current Word for Mac versions do not provide a setting to disable the floating Insert Comment button. There is no workaround as well as of this time.
I suggest to log a feedback directly to Microsoft (if there is an existing topic same as this you can upvote it) Go to Help> Feedback in the Word menu bar. Feedback goes directly to the respective development group.
This is the best method for submitting comments, complaints, or feature requests, etc.