Read prefs: C:\Users\thinsoldier\AppData\Roaming\Blender Foundation\Blender\2.91\config\userpref.blend
WARN (bke.anim_sys): C:\b\buildbot-worker-windows\windows_291\blender.git\source\blender\blenkernel\intern\anim_sys.c:2926 BKE_animsys_eval_driver: invalid driver - cycles.preview_denoising_start_sample[0]
I get this message and the main window never opens. I have to force quit Blender and run it again and hope it works.
If it does work it takes over 40 seconds before I can use Blender.