I use CC 2018 on my laptop and have a 27"' Samsung monitor on which I edit. My photos in PS looks bright and vibrant, but as soon as I save them as Jpegs, they look bland, dull and desaturated on my monitor. What settings should I use?
That has nothing to do with "saving to jpeg". It has to do with what application you are using to view the file. If it isn't color managed, Adobe RGB and ProPhoto files will look desaturated. If you convert to sRGB, the difference will be much less noticeable (but still there).
Don't change anything in PS color settings. That's not where the problem is - in fact, it's probably not a problem at all, just lack of proper color management in your viewing application.