As you know, when you share a document stored on SharePoint Online, the default mode is in Edit which can lead to unintended edit of the document.
An update is being deployed (expected to be completed by end of May) which will allow you to set the default mode to Review, limiting editing actions to only comments or tracked changes.
This change will only apply to Word document.
The next time you share a Word document and want to set the opening mode to Review, check the option Allow editing is unchecked (the option is available from both Word on the Web and Word client)
People who open the document in the Word desktop app instead of on the web will only be able to view the document. They’ll see a notification to switch to Word for the web if they want to make changes.