Unfortunately, of all the available/popular data sources that are available, Excel is the most limiting and most fragile. When other users modify Excel files that are used by an app, they can easily 'lock' the file or corrupt the file.
If possible, I would recommend that you and your clients use SharePoint instead (if this is a viable choice). SharePoint provides a more robust data store, and it is cost-effective because it is included in most of the Microsoft 365 plans. Otherwise, it is best to recommend that users do not modify the Excel file outside of Power Apps.