Lightroom Classic stores all edits in its catalog database, separately from the original image files which are left untouched in full original quality. That’s why the originals are still unedited. To use a version containing Lightroom Classic edits, it has to be exported.
So to get what you want, do a quick export of the image (File > Export), drag the exported copy from the desktop, and drop it into Apple Messages.
If you do this a lot, you can create an export preset all set up for the file format and size you want images to be for messages. Then, when you want to include an edited image in a message, just select that preset (File > Export with Preset, which you can assign a shortcut to in macOS) and pick up the image.
I like to select the Show in Finder export option (under Post-Processing) so that Lightroom Classic automatically switches to the desktop when it’s done exporting, then I just drag and drop into Messages.