Funny enough, 15 minutes after I posted this question, I found a workaround 😅 But yes, all the levels were on. I have here 2 layers of liquified art, and sandwiched between them a photo. Each both liquified art had level and hue adjustment layers on top of them. I wanted to adjust the liquified layers without affecting the photo, as you can see above.
Here's what I did: for each liquified layer, I created a new transparent layer below it. I selected the pixels from the liquified layer, and painted that selection black in the new transparant layer. Then I merged all 4 layers for each set of liquified art.