Lights Out mode not working.

Hello, I have been using Lightroom Classic since before the split, and have never run into any issues with Lights Out mode previously. But for the past three or so weeks, LR will not dim my screen. The window says I am in the correct mode and that the windows switch every time I hit "L," but no dimming occurs. When I restart LR, it works normally for the first couple of tries, but then, all of a sudden, it stops working again. Any advice? My workflow is crop + color/exposure correction in LR -> PS for final touches. 

15-inch 2019 MacBook Pro running Sonoma 14.5, LR Classic version 13.4.