How can I stop her from getting on my desk?

Gracie is my 8 year old long-haired cat and she lives in my bedroom basically 24/7 with her litter box in the bathroom. She is allowed to be anywhere in the room, but she knows I don't like her getting on my desk with my fragile OLED monitor (a stiff wind can cause scratches) and leaving pawprints, fur and litter crumbs on the desk mat and surface itself. She is aware that I don't like it, so she only jumps up there when I'm not in the room.

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Her chosen place to sleep right now is in my chair when I'm not in it, in which case she is on the bed. I understand the desk is the only access to one of the 3 windows, but she rarely gets in the window and I leave it open all the time. It has a screen, obviously.

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I bought her a cat tree tower thing with lots of places to sleep and toys to play with and I'm hoping she'll choose that instead. I can move it around but I want to put it right next to the desk and window. Knowing cats though, she will still jump up on the desk and I just want her to stop. I'm tired of cleaning the mat, getting fur out of the keyboard, and she has spilled two drinks since I've had this set up in January.

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What's the best way to deter her? Some sort of scent localized to the desk that she doesn't like? That's my only idea. I'm going to build her tower soon and I hope she loves it and I would love if she used that, my chair or the dresser to do her feline things.