You can disable Teamviewer from launching every time your computer loads within the settings of Teamviewer.

If you want to know other places that can launch programs at startup (apart from the 'Startup' folder in your start menu), you can check the registry, as there are directories in the registry that launch programs upon boot.
The registry directories are:
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
(And sometimes: HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\RunOnce and HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\RunOnce)

These contain Keys that point to files that are executed at boot.

The more simple way is to type in the run bar msconfig from there there will be a list of all programs that run upon start up

Edit: That said list is the start up tab at the top.

Edit2: Just read you said its not in the start up tab either. Thats odd. are you referencing the tab in the msconfig menu? Thats where it should be and I have Teamviewer as well on multiple computers and thats where mine is at.

You can use a tool called 'Auto Runs' for windows which gives you a extensive look into everything which starts up, with this you can easily delete or disable the teamviewer startup entry.

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