Hi Lauren, In Finder, search your drive(s) for a file ".lock" You will probably find one in the folder where your lightroom classic catalog is located. If you find one, delete/trash ONLY that file which ends in .lock. Then your Lightroom Classic should start normally. Check back to let us know if that fixed it for you.
@Lauren Lee Photography That's one I'm not familiar with. If LrC runs OK under another user, then I'm not sure if un-installing and re-installing would help. Still if it was my machine, I would un-install through the Adobe Creative Cloud app, run Adobe CC Cleaner and re-install. You have nothing to loose except time by trying that. While I have been using a MacBook Pro for about 6 years in addition to my main PC, I am not familiar enough with Mac OS to recommend anything else.
Of note, the .lock files are created when LrC opens and normally deleted when LrC is closed. If the computer is shut down without properly closing LrC, the .lock files will be left on the drive to cause a startup problem later.