I make this all and it works now
Taskkill /F /IM outlook.exe
Taskkill /F /IM ms-teams.exe
xcopy G:\Support\Teams\TeamsMeetingAddin %LocalAppData%\Microsoft\TeamsMeetingAddin\*.* /S /Y
%SystemRoot%\System32\regsvr32.exe /n /i:user %LocalAppData%\Microsoft\TeamsMeetingAddin\1.23.28501\x64\Microsoft.Teams.AddinLoader.dll
reg add "HKCU\Software\Microsoft\Office\Outlook\Addins\TeamsAddin.FastConnect" /v LoadBehavior /t REG_DWORD /d 3 /f
In these cases, it's not about re-registering the Add-In DLL. It's simply not present on the machine in the first place, and we shouldn't have to do your workaround, so I've logged a ticket with MS support. First response was "are you sure it's not there?", followed a few days later with "have you tried uninstalling and reinstalling Teams?"
If anyone else with Unified Support can log a ticket and get some heat onto this issue, it'd be great.