To install Teams on Windows 10 LTSC, you'll need first to allow the trusted apps to be executed

- Install the WebView2 Runtime or (or Edge which contains WebView2)
Allow MSIX sideloading:

 reg add HKLM\SOFTWARE\Policies\Microsoft\Windows\Appx /v AllowAllTrustedApps /t REG_DWORD /d 1 /f

Download the MSIX package from Microsoft:
https://go.microsoft.com/fwlink/?linkid=2196106
Run the following command to deploy the package:

Add-AppProvisionedPackage -online -packagepath "C:\temp\MSTeams-x64.msix" -skiplicense