RAW+jpeg dual format is imported into lightroom, and photos only show raw. What happened?

Edit-Preferences-General-Import Options, and check "Treat JPEG files next to Raw files as separate photos":

The JPEG file next to the Raw file is taken as a separate photo, which is suitable for photographers who take Raw+JPEG photos with their cameras. Select this option to import JPEG as a stand-alone photo. If this option is selected, both Raw files and JPEG files are visible and can be edited in Lightroom. If this option is deselected, Lightroom will treat duplicate JPEG as an attached file, and the displayed Raw file will have an extension of +jpg.