In the File Settings section of the Export dialog (Command-Shift-E [PC: Ctrl-Shift-E]), you get to choose your file type (JPEG, TIFF, and so on), but it’s making the right Color Space choice that determines if the colors of your image look pretty much like you see here in Lightroom, or whether they’ll be pretty much messed up. I’ll make it simple: choose sRGB for posting images to the web. They’ll look the closest by far to what you’re seeing onscreen in Lightroom.
This tip originally published in How Do I Do That In Lightroom Classic? 2nd Edition by Scott Kelby.