Adventures across the 3rd dimension

It's still not appearing unless I actively keep pushing F9 (and most of the time it just flashes on screen and disappears again, unless I click it before I release the F-button...)

Does it behave that way if you access it from the menu?

I can't even find it on the menu. But I realised it closes as soon as I "mouse out"...
It used to open every time I added a new mesh and every time I moved something. Now it won't appear at all unless I press F9

I wonder what Merlin stepped on this time?

Just tried and it behaved the same for me in the menu too.

Is there a small circle with a + in the bottom right corner of the viewport window?

Not that I can see... Why?

Sometimes when tool options get moved off-screen beyond the window borders then that little button appears to bring them back but if it's not there then it can't be that issue either.

Everything I google says either to use f9 or the menu, but neither of those options makes it appear automatically when I create a new shape. I've also looked through preferences and keymapping and various options and I can't find anything that seems to have anything to do with this parameter window... I did find that F9 is mapped to "redo last action" or something like that, which seems a wee off?

Well, I'm too tired to bother any more with it tonight.

I think I've worked it out!

There's a checkbox in the smaller View menu. I think you might have accidentally clicked.

 

When it's unchecked the the little thing does indeed disappear.
And as well as being called the Parameter Window/Panel it's also sometimes called the Operator Box.

Checked or unchecked, makes no difference to me

If you create an object (like a torus), then perform some other operation (such as just deselecting it), then it is no longer a torus, it's a mesh object and those initial parameters aren't available any more.

As far as I know the panel only allows you to adjust the settings of the last operation, so the initial parameters of the object wont be available if you have performed several operations since then. You would need to undo back to the point at which it was last available (i.e. the moment of creation).