In my experience the Meta key is right (and sometimes left) Alt. That’s from Emacs, etc. But Emacs got it from an old keyboard lay out. VT100? I recently purchased a keychron K5 Max with 108 keys. I haven’t had a keyboard with the traditional keyboard layout in a long time because I’ve been on a laptop. I used to be able to type without looking at the keyboard at all, since the key location was standard. The keyboard is mechanically wonderful, but the backlighting doesn’t illuminate the key markings, which is the whole reason I wanted backlighting.
The keyboard comes with swapalbe keys so it can conform to either Mac (default) or Windows (who cares?) markings. The key others are now calling “Meta” is marked “Option” and what is “Alt” in the Windows world is the ‘shamrock’ key.
On my computer, the META key is at bottom left, just right of “CTRL”. You have “Option” in that position. On all recent computer here, that key has a “Windows” logo on it, and I have usually called it the “Windows” key.
I never much liked that key, but then I never liked Windows. But it does bring up the menu for me in openSUSE/KDE.
Ironically, the Plasma key combination to activate rectangular screen-scraping is ‘Meta+Shift+Print’ (double-click to commit.) Which is not the same ‘Meta’ of Emacs. In the case of Plasma Meta is Win/Option.
You’d have to ask the people who named it.