I have found, very simply, how to do this with Mac, but not for Windows. Can anyone advise? I saw something that said "Edit > Preference > General > Optimize for screen" or something like that. But that option doesn't exist in Lightroom CC (as far as I can tell)... THANKS!
Can you please tell us your target or what you are trying to achieve?
Your OS version as well as the exact version of LR would possibly be helpful too.
I heard that setting LR to "open in low resolution" mode helps it to run faster. But I only see how to do it on mac. How do I set it to "open in low resolution" on windows 10 is my question (latest update of LR CC)
"Latest" usually is not. What version number of LR are you using?
In LR 6/2015, you can optimize the standard presets to be no larger than your screen needs.
menu: / edit / catalog settings / file handling /
set the "standard size" to "auto".