All good points. On the computer I compulsively use the post it notes. I think one of the Booker short list authors writes on actual post it notes -
https://thebookerprizes.com/the-booker-library/features/paul-harding-interview-this-other-eden
I have a very old Kindle I rarely used that I got second hand to see if I would use much. If I recall correctly, it also has a feature to see what other people have highlighted? I think on one book I deliberately under-lined loads of pointless things, to subvert the system!