I beg your indulgence. I am confident this isn't an Emacs problem, let alone an org problem, but my eyes hurt from searching for an answer, and this list, the only one I subscribe to, is populated with gurus. I promise never to use it this way again.
OS: PopOS 20.10, DE: GNOME 3.38.2 WM: Mutter GNU Emacs 26.3 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.14) M-S-$ does not spellcheck word. It will work from the menu bar, and it will work if I drop into a tty and run Emacs. Emacs gives no response in the minibuffer in the GUI when I press M-S-$. M-x describe-key M-S-$ does nothing. C-h b C-s 'spell' reveals that indeed M-S-$ is bound to spellcheck word. And other M-S- keys work like M-S-> just fine. There has to be some keybinding outside Emacs taking precedence. I have gone through dconf-editor until my eyes bleed. Done gsettings list-recursively org.gnome.desktop.wm.keybindings | sort | more and gone line by line. I have done dconf dump / > dconf.dump and read through them all, in addition to checking PopOS' keybindings in Settings. And trying a different keyboard. Nothing in Tweeks, dconf, or Settings uses M-S-$, but I disabled anything that uses Shift anyway (nothing uses $). No joy. I don't want to rebind it for this machine only, nor do I want to go through the hassle of installing a different DM/WM. StackExchange, et.al are full of problems with the the M key, but not one specific keychord only. Any ideas? I will accept rebukes. I'm desperate. TIA! Bo Grimes