Like many others in the thread, after opening the back cover, disconnecting the battery and cleaning out the dust with brushes and compressed air, the high cpu usage when using an external monitor seems to have decreased. Helpful youtube videos: https://www.youtube.com/watch?v=KyMjUCB-hhU : this was way more difficult than i expected. I felt i should have just gone to an apple store when doing this https://www.youtube.com/watch?v=tBrKXhkfnAE : this video goes into removing a lot more things than just the battery to apply thermal paste, i didn't do any of that - can be risky to remove and replace a lot of parts. in my case my macbook didn't turn on after i put the back cover on initially and i was freaking out a bit. But it turned out i didn't connect the battery wires properly, i didn't need to lift the 2 small plastic clips for removing the black wire with the S pattern initially, but that lead to the ends not being connected properly when i put it back. the lesson was to follow the video very closely. Tools i used: Brushes: https://www.amazon.com/dp/B074LZ649V?psc=1&ref=ppx_yo2ov_dt_b_product_details Screwdriver: https://www.amazon.com/dp/B07TXFYP5G?psc=1&ref=ppx_yo2ov_dt_b_product_details