Orhan,

Just FYI, this add-on is compatible with 2021.3 and, in addition, does have help/usage information packaged with it that you can access via gaining focus the add-on in Add-Ons Manager (NVDA + N, T, A, Enter) then activating the Add-On Help button.
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Brian - Windows 10, 64-Bit, Version 21H1, Build 19043  

The ignorance of one voter in a democracy impairs the security of all.

         ~ John F. Kennedy