You have installed Microsoft Office on your computer. Whenever you logon to the computer, you see a Microsoft Teams splash that asks you to login, which you have to close every time if you choose not to login.
You can go into task manager, click the "Startup" tab, click Microsoft Teams, right-click and disable. However, this doesn't work permanently as it will come back if you update or reinstall Office. Also, other users who login to the computer will still get the Microsoft Teams thingy loading automatically at startup.
REM Delete Microsoft Teams Auto startup reg key
reg delete HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run /v "com.squirrel.Teams.Teams" /f
Now every time someone logs in, the Teams startup will be automatically removed, so that will be the last time they see it.