Lightroom Classic won't start

You may be experiencing the issue described in the thread I linked below, which is located on Bugs forum. Others have managed to get LrC running by following the instructions provided in the pinned reply just under the first post. 

https://community.adobe.com/t5/lightroom-classic-bugs/p-lrc-12-2-1-fails-to-start-launch-or-is-extremely-slow-launching/idi-p/13673512