I don’t think that existed back in the day, I could be wrong though. I’m thinking 1998-1999 era iMac personally.

It was definitely present in MacOS classic can’t tell exactly when contextual menu was added. But on top of that there was actually a third method, select the disk (highlight) and press cmd-E. Which now now that I think of it is just a shortcut for the fourth one, select the disk then select "Eject" in the file menu. Actually this last method must be the mother of them all, the drag to trash was also maybe one of the first "discoverable shortcut".

It’s just that "drag to the trashcan" gimmick was present since first Macintosh introduction keynote in 1984 and is still usable as of today so no surprise it’s the first answer on every Q/A.

I can’t yet skim through the footage but it might even appear in the 1984 LIVE DEMO (more emphasis needed) of the first Macintosh : https://youtu.be/1tQ5XwvjPmA

The trash can method is how you would of ejected the CD in OS 9, but back then there was also an eject key on the keyboard.