Please try to launch SSMS directly from the executable file. You can do this by navigating to C:\Program Files (x86)\Microsoft SQL Server Management Studio 20\Common7\IDE\Ssms.exe and running it from there. Please run it as administrator. Remind temporarily disable any antivirus software during the installation process and enable it again after SSMS is installed.
If launching directly doesn't work, please make sure the directory C:\Program Files (x86)\Microsoft SQL Server Management Studio 20 does not exist before reinstalling. You can delete it if it does.
And run the following command from command prompt to delete the registry key: reg DELETE "HKLM\SOFTWARE\WOW6432Node\Microsoft\Microsoft SQL Server Management Studio" /reg:32. After doing this, restart your computer.
If all do not work, please check the SSMS installation log located in the SsmsSetup folder under %TEMP%, and share the setup log to us for further troubleshooting.
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