The default "drop stack" keybind is ctrl + q on Minecraft. On a Mac, since the "command" key functions as ctrl does on Windows, it conflicts with the ability to drop stack as the default bind is command + q, which is also the Mac keyboard shortcut to "quit application" that cannot be changed. Luckily, Lunar has a solution for this, which ended up being my reason for switching to Lunar after years of using Labymod on my Windows PC. In Lunar's settings, under controls, I was able to change the button that needed to be held to "drop stack" from command to ctrl; however, it only works if you want to drop a stack from the item you are holding in your Hotbar. I believe this feature is intended to work if you hover over the item in your inventory with your mouse and try to drop stack as well, just like the vanilla ctrl + q keybind works. I looked through #1215390637705396306 and #📋︱community-support and did not find anything about this.
I guess I'm suggesting parity between the vanilla "drop stack" keybind and the Lunar client's bindable "drop stack" keybind.