What is the ”I” who watches what the mind does? When reading about philosophy of mind, I encounter expressions like ”I (or we) think”, ”I percieve”, ”I remember”, ”I see red”, ”I feel pain” etc. Isn´t it the mind that performs these actions, not the "I"? What is this ”I”? Is it some separate compartment of the mind, identical to the mind, or outside the mind? Should we modify Descartes and say: ”The mind thinks, therefore it is”?

I'm not sure I'm getting your second question. Why should the I that says 'I feel pain' be the mind and not the I? Unlike Descartes, who thinks that both of these things are the same as consciousness, and as himself, not to mention his soul (Berkeley makes these equations too) I would prefer to reserve the words "mind" and "mental" to describe two things that are not me. (i) The intellect. We say, 'He has a good mind' and things like that. (2) The imagination. We say, 'It's all in your mind; you're just imagining it. Snap out of it.' The mind and the imagination are two different things, obviously. But neither of them is me. What is meant by "I" and "me" and so on? It certainly is not the same thing as "mind", and nor could my mind, in my two senses, be me. I have a healthy appetite, especially for Italian food, but the same is not true of my mind or imagination. I have just had lunch. But my mind and my imagination, poor things, never eat. So neither of them is me. They are things or whatever that I have. I have a mind, and I have an imagination, just as I have an arm and a leg, though my intellect and my imagination are philosophically more interesting than my arms and legs. So far as I know no-one has produced a book on The Philosophy of the Leg. There may be something out of whack with the question 'What is the mind?' Some people (Anscombe, famously) take the view that "I" is not a referring expression. It certainly is not the name of me or anything else, and even more obviously it is not a proper name, in spite of the capitalization. Anscombe's line, following Wittgenstein, is that if a speaker S says 'I like such-and-such', this is true only if S likes such-and-such. And clearly it is not true that if S likes such and such, I do. You might have a look an Anscombe's rich "The First Person", available online, to get started on this amazingly interesting topic.