Please go to the location where the catalog is saved (the Pictures folder of your computer by default), and check if you have a file with the same name as the catalog ending in ".lock". If you do, delete the file and then try launching Lightroom Classic again.
Please go to the location where the catalog is saved (the Pictures folder of your computer by default), and check if you have a file with the same name as the catalog ending in ".lock". If you do, delete the file and then try launching Lightroom Classic again.