As someone who never quite reached this level myself, I feel like it's when you start being able to think in the second language inside your head.
I only got to the point where I had flashes of this happen for specific topics that didn't translate well. For everything else I kept thinking in English, even if I then needed to convert it back mentally after.
I'd like to point out that a lot of the world doesn't even have separate (or even any) devices for drying. Especially areas like the Middle east, Africa, and Asia. It's still very common to hang dry clothes in many warmer climates. Japan for example doesn't use them very much because electricity prices are so high and space is so limited. They may also just be a combined washer and dryer unit in one that does both functions due to a lack of space.
https://www.researchgate.net/figure/Household-ownership-of-electric-clothes-dryers-in-select-countries_tbl1_345758611