If you are talking about 'Layer Explorer' which lists all of your scene elements and layers then that just "tears" off. You left-click and drag the top just below the double dotted top edge border. You can pull it off onto your main screen. It will have an 'X' in the corner, just click that and it's gone. If you want it back go to the 'Tools' menu and click on it in the top part of the list.
However, if you grab the top of the 'Layer Explorer' and drag it to the far left, the left side of Max will turn blue and open a hole you can drop it into. Then it's nested neatly on the left out of the way. It's good to have that always available as you build scenes, especially if they get complex. You can resize it by hovering over the right edge of it and dragging to minimize it. Then if you need it, it's still right there.
But fortunately, Max gives us all ways to set it up like we want to. So if you want to leave it off till needed, no problem there.
Rob Holmes

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3ds Max (2023-2025), V-Ray 6.2, Ryzen 9 3950-X Processor, DDR 4 128MB, Gigabyte Aorus X570 Master motherboard, Sabrent Rocket NVMe 4.0 M.2 drives, NVidia RTX 4090, Space Pilot Pro, Windows 11 Pro x64, Tri-Monitor, Cintiq 13HD, Windows 11 x64
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