First of all I’d like to point out that this is no way a negative criticism, but rather a genuine attempt to make unity better for new users…
I spent more time that I care to admit with this one, basically because all the post at various places were pointing at other related issues not this one.
Basically on a UI event I was attempting to drag and drop a script itself, rather than a game object.
The problem being when you do drag a script onto the on event list you don’t get any feedback and worse still you can even use a text box next to the script (with unpredictable results in the box to the left of it…
Its obvious now that what’s needed is the actual instance of a script (hence the need for the GameObject) I was quite delighted when the textbox turned into a drop down !!
I think it would be a quick and very worthwhile “fix” to throw up an alert if a user tries to throw just a script into the on event list.
I’m currently using the 2021 beta on Ununtu Linux LTS btw (and loving it!)