I used to be able to hit Cmd-backtick (the symbol just below ~ on my Mac keyboard) to switch quickly between the RStudio source editing pane and the console. Like so:
However, it doesn't work anymore in RStudio 1.2.1153.
Also, if I try to recreate the same shortcut, the Keyboard Shortcuts dialog doesn't seem to want to accept Cmd-backtick as a keystroke. Is that disallowed now? Is something in my OS (High Sierra 10.13.6) blocking the input?
Yes. Cmd+Backtick is a MacOS shortcut for cycling between the open windows of an application; if RStudio has an additional window open (e.g. if you've popped out a source window or the Plots pane) you can use it to switch between those windows.