To be fair I gave the new UI another chance and play again through it:

First thing I did: "Hide Ribbon Bar"
That works but I cannot activate it again!

Right Click in any space up/left / middle / IC sign... nowhere is a button "show ribbon bar"

I even cannot get back to the old UI
And with close IC ...IC saves that version!
HELP!

That was a short Test!

CTRL SHIFT R

Then lastly Ctrl-Shift-F9 to switch back to the toolbar UI.

Thanks to you all.

Maybe you already know what comes up now

Suggestion:
when I want the ribbon bar back I need to right click in the scene to get the button "show ribbon bar" (nobody knows that short cut)
...or
...right click on the IC sign upper left.
...or in the grey upper bar.
Somewhere it has to appear!

Then:
The big IC button (upper left) should stay as it is when to hide Ribbon; ... as this is the way to do all commands.
Today it shrinks to a small button with near to no functions.

Thanks
Carlo

so how is it going with the new UI? I tried it again and it took me a little over 5 minutes with all the extra clicks to go back

True, it did take me more than 5 minutes to appreciate the changes.

Started IC....Ribbon UI displayed...Interesting.....when I closed IC the last time I was using the "old-school" UI.

CTRL SHIFT R

Bam! Both UIs!

Or am I confused???

You are able to run both UI's. Ctrl-Shift-R brings up the Ribbon UI. That is not the toggle between the two.

Cary