How is it possible for anyone to spy for an Android phone without using spying apps?

Can a “bad man” spy on an android phone without installing spy apps (those apps that require payment)? By “spying”, I am talking about utilizing logger that is key screenshots, l k over communications and so on.

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Can you really spy on an android without the need for spy that is such? Can there be another real means somebody can spy you?

Does “unknown sources” have to be fired up for spyware become installed?

Can someone install some type of spying software or are spying apps the only way?

Suppose the “bad man” has physical access to your Android os device, simply how much time would that person need so as to set up some form of spyware?