Best Approach to generate Users Permission Matrix report for specific all Site Collection in tenant

Hi bhartisemwal1990​ 

Thanks for reaching out.

Currently, there isn't an out-of-the-box feature to generate a permissions matrix or report for all users across the entire SharePoint tenant. However, SharePoint does provide a built-in Permissions Matrix Report for individual site collections, which gives detailed permission information for that specific site.

You can generate the report by following these steps:

1.Open the SharePoint site and click the Settings (gear) icon.

2.Select Site usage.

3.Scroll down and click Run report.

4.Choose a location to save the report (for example, Documents or Site Assets).

After a few minutes, the report will be generated and saved in the selected location. You can then download and review the detailed permissions report for that site.

Please refer to the screenshots below for reference.