P: Weird "Quick mask" when I click on layer thumbnail after drawing directly on mask

I often alt+click on a mask thumbnail to view the mask and draw on it directly. Then I click back on the layer thumbnail to see the results. This always used to work fine. But since a recent update, now when I click back on the layer thumbnail, it's like I've added a "quick mask" with a red overlay. I can not for the life of me figure out how to turn this off. I randomly click on other layers and eventually it goes away.

What is happening here, and how I turn this off? I've tried clicking the "quick mask" icon in the toolbar and that does nothing. Also the Q shortcut does nothing. Windows 10, photoshop version 24.0.1

Thanks in advance for any help!