As noted above, the option was removed in 3.2.3 for installations on macOS 11 and greater, because changes in the OS prevented Scrivener’s ability to disable the blinking. The option is still available on earlier versions of macOS. The settings in Scrivener’s preference file thus will work on earlier Mac systems and do nothing on later ones.
That said, there’s a system preference for adjusting the blink interval that will affect various apps using Apple’s text view, including Scrivener. So on Monterey 12.6.5, I was able to essentially disable the insertion point blinking in Scrivener using the following global settings in Terminal:
defaults write -g NSTextInsertionPointBlinkPeriodOn -float 3600000
defaults write -g NSTextInsertionPointBlinkPeriodOff -float 0
Time is in miliseconds, so it blinks once an hour with the above example.
To revert:
defaults delete -g NSTextInsertionPointBlinkPeriodOn
defaults delete -g NSTextInsertionPointBlinkPeriodOff