Running Win11 OS, Lightroom 6, Unable to unlock catalog, tried deleting lock file, tried creating a new catalog it gets immediately locked, tried uninstalling then a fresh reinstall creating new catalog then that is immediately locked!
What error message do you get?
Are you able to use Lightroom 6 when this happens?
What indication do you have that it's locked?
Is it possible you have multiple catalogs and did not delete the related lock file you thought you did?
Try resetting the Lightroom 6 preferences. Uninstall and reinstall does not reset the preferences. I think with Lr 6, to reset preferences, you have to find the preferences folder and rename it or delete it.
Please let us know how the preferences reset goes.
This is unlikely to be caused by the .LOCK file. This is something else.
If preferences don't fix the problem, I would try unzipping a recent backup catalog, placing it in a brand new empty folder, and opening that backup by double-clicking on it.