I am currently using the latest Haiku nightly on VirtualBox but if I try to stack or tile it doesn’t work. I have read the guide (at https://www.haiku-os.org/docs/userguide/en/gui.html#stack-tile ) but I can’t. Also, I don’t know what key is ‘OPT’, but I have read that it should work using the ‘Windows key’.
Woks perfectly here on today’s nightly and yes, I do use the “Window” key. I suggest you look at the Keymap Preference applet and see if you haven’t accidentally selected a keyboard without that key.
Or a keymap where the right OPT key was moved around because of our lack of support for a separate AltGr key.
On a french AZERTY keyboard with the default keymap, OPT is either left “window”, or AltGr. But right window is CMD, same as left Alt. So, look at the keymap preferences to identify your OPT keys.