Hello, Steve Larsen2,
Welcome to the Microsoft Community!We truly appreciate the information you’ve provided and understand the inconvenience you're experiencing with the installation prompt for Microsoft 365 Word each time you start Word 2011 after your purchase of Microsoft 365. This situation undoubtedly causes you some trouble. Please rest assured that we take your issue seriously and are committed to doing our utmost to assist you.
First, I would like to explain that once Microsoft 365 is installed, the system automatically recognizes and prioritizes the latest version of Word. Therefore, when you attempt to use Word 2011, the system continuously prompts you to install the Word version of Microsoft 365.
Microsoft Word for Mac 2011 - Microsoft Lifecycle | Microsoft Learn
I understand that you still wish to use Word 2011, but I must remind you that Word 2011 has reached the end of its product lifecycle. This means that Microsoft no longer provides technical support, bug fixes, or security updates for it, and its features are not as comprehensive as those in the Microsoft 365 Word version.If you want to install the Microsoft 365 Word version, you can download the standalone installation package from the official website: Update history for Office for Mac - Office release notes | Microsoft Learn
I also understand that you may be concerned about continuing to use Word 2011. Given the potential compatibility issues between the two versions of Word, you might encounter some problems during usage.If you’re worried this might affect the book you are currently writing, we recommend backing up your files to local or cloud storage services first. After that, you can open the backed-up files using the Microsoft 365 Word version and continue your editing work.We look forward to helping you smoothly transition to the new version of Word and ensuring your work is not affected. If you need further assistance with these steps or have any questions, please feel free to reach out to us.
We wish you a great day!
Navian - MSFT |Microsoft Community Support Specialist