Windows – How to find Skype in Windows automatic startup

I'm currently trying to rid a Windows 10 computer of all unnecessary automatic startup programs, because it had problems with being terribly slow even without starting any programs manually. One such program appeared to be Skype, which somehow manages to avoid being listed in the Task Manager "Startup" tab. So, I tried looking for other ways to find startup programs.

To get a full list, I found recommendations to use Autoruns for Windows, which is a Microsoft product, so I'd expect them to make something that knows their own system. Turns out, Microsoft is unable to detect their own programs' startup status. Even though Skype does automatically start up on boot (I can call skype without first starting it, and it does immediately ring after booting the PC), the Autoruns program doesn't detect it at all (I couldn't find it manually, nor did filtering to 'skype' result in anything).

This concerns me a bit, because if Microsoft is able to make something that avoids all detection, how can I be sure there's nothing else more malicious that can do that?

So my question is in short: In what location could I look to make an actual exhaustive list of all programs that start on boot, including programs like Skype?

Edit: I am not looking to disable Skype from its internal settings, I want to be 100% sure that nothing is able to start itself without permissions. Disabling Skype only solves this problem for Skype, but eventual malware ending up on my pc would then perhaps also fly under the radar. I'm using Skype as an example of what is possible for something to do, so I want something other than Skype itself to stop it from starting.