During my years with macOS, I have sometimes seen ways to mark text vertically. At some point, I saw information on this that seemed official, but I can’t find it anymore.
To me it is a function worth a lot, that have come and gone since the 90’s. But at the moment I don’t see any application that supports this.
I wish for a system wide way to do this, but I guess there’s not. Are there any apps that support it?
See attachment for a better explanation
This is also known as block selection some places - that might help you find some third party solution.
If I understand what you’re looking for, TrialPad on Mac and iPad can do something like this (free-floating highlights, basically), but it is part of a litigation package that runs $300-$400 per year for a subscription, so unless your requirements fit a specific need (TrialPad is excellent for anyone who needs to present information to people live or via Zoom), it is pricey. And it isn’t something that overlays the Mac screen generally, but rather works on PDFs you load into the app.
Lots of coding editors do.
Textmate is one I use a lot. It’s free.
If I need to do any editing to amount to anything, I have a Keyboard Maestro macro that copies whatever I have highlighted, opens Textmate, and pastes into a new document. I do my editing there, Cmd-A to copy all, Cmd-Tab to switch back to the original app, and Cmd-V to paste over what was highlighted. Easy peasy.