Hello,
I am EngineTyme, an independent advisor who will be willing to assist you on this request. Note that I am a user like you and not a Microsoft employee or staff.
You can follow the steps suggested by Mia Zhao MSFT for resolving Word files not saving on Mac in this thread: https://answers.microsoft.com/en-us/msoffice/forum/all/word-on-my-mac-wont-save/089c589c-884b-4180-b296-aae574c12bf7
"1.Clean the Word cache folder.
Quit Word app from dock bar and then open Finder > press Command + Shift + G > input ~/Library/Containers, remove Microsoft Word(or com.microsoft.Word in Catalina) folder to desktop. Then, restart Word to check if the save/close action will be faster.
2.Run Mac in Safe Mode.
This can help us to exclude any possible influences from other third-party apps or background programs that may have a conflict with the Excel app. See: How to use a "clean startup" to determine whether background programs are interfering with Office for Mac (microsoft.com): https://support.microsoft.com/en-us/topic/how-to-use-a-clean-startup-to-determine-whether-background-programs-are-interfering-with-office-for-mac-e99e92b2-f67e-b98d-b69f-d12236c53f2c and kindly refer to the Apple article in the last one to get detailed steps.
3.Reinstall Word to the latest version.
Go to the Applications folder and drag Microsoft Word.app to the trash. Then restart your Mac, download the latest version of Word from: Update history for Office for Mac - Office release notes | Microsoft Docs: https://docs.microsoft.com/en-us/officeupdates/update-history-office-for-mac."
Please let me know if further assistance is required.
Best regards,
EngineTyme.