I have a laptop with Windows 10. If I go on settings and then privacy there is a list of apps with the information about their permission to use my camera (I'm talking about the built-in camera, not an external device). If I disable all of them then should I be secure about the fact that there is no way someone is spying on me? If not, what could I do?
There are 2 levels of access
Software: The only thing that the Windows 10 Privacy settings protect against are the Windows API calls for Webcam. So if you only use official microsoft apps and or apps from the windows store you are indeed safe from abuse (they all utilize UWP that uses sandboxing and in there you need to use the tools that also show up under the privacy settings of windows).
If you use any Virtualization / custom build / non-store applications than all of those could utilize the low level syscalls to talk with the camera directly bypassing the lockout windows has on the webcam.
Hardware: If you use any recent AMD / INTEL CPU that has any of the remote management tools in them (Intel AMT wiki) than not even your OS has final control over your hardware, the Management tool does. This means that anyone with access to it has complete control over your system and there is no defense possible besides completely disabling this system (not easily doable on all hardware)
In short it depends highly on what level of "certainty" you want to have, and what type if risk you are willing to take.