It is not possible to copy and paste out of serial monitor. (Apple Mac) - It was possible on 1.89
How exactly are you trying to do the copy ?
What is 1.89?
Please ignore the rest, confused with the output Window 
I'm not an Apple user, does it have a context menu (right click)?
For RC9.2 in Windows
Windows here though. No, there is no copy or past or even a context menu in the Serial Monitor (will most likely eventually come).
However, I highlighted the required text in the Serial monitor and used Ctrl+C to copy then CTRL+V to paste into Notepad++. CtrL+Ins to copy and Shift+Ins to paste also works.
Has there ever been ?
What do you mean by 1.89 ?
In IDE 1.8.16, my latest version) - not in the receiving panel. There is a context menu in the transmit top frame (for some reason - probably more for the "paste" option). That context menu is also available in the IDE 2 serial monitor top "entry" (?) line. This obviously implies the IDE 2 serial monitor behaves the same as in IDE 1.8.x.
I never mentioned 1.89. The OP probably meant IDE 1.8.9. And no, it was not available in the receiving panel of the Windows serial monitor.