In Emacs 29 with company-mode, I have gotten stuck using find-file in the mini-buffer when creating a new file in that completion only offers what exists and C-g quits find-file, <return> will replace input with the selected/default completion. The answer is simple, but not documented anywhere I could find, vertico-exit-input !

I've been reinventing my emacs configuration with Emacs 29 and replacing/adding features. One of them is company-mode, which is complete-anything (anywhere or everywhere), which works remarkable well. Except for one scenario, opening a new file. After C-x C-f, in the mini-buffer with "Find file" mode, company-mode offers completions for what exists. When typing a name that does not exist the mode does its best to match something/anything. At this point there is a default completion so pressing RET will drop the input and send the completion. Pressing C-g (the way to do company-abort elsewhere), aborts find-file. After various attempts of adding to a keymap (see my useless attempts below), none of which worked, while find-file was active I did C-h b which lists all the bindings in effect. I found that vertico-exit-input was bound to M-RET. No knowing what that function actually does, I tried the key and it did pass my input to find-file.

What is vertico-exit-input you may ask, as I did? Help says:

vertico-exit-input is an interactive byte-compiled Lisp function in
‘vertico.el’.

(vertico-exit-input)

Exit minibuffer with input.

and that describes what I wanted. Another case of not knowing how to ask the question to get the answer.

These bindings did nothing of use, but may be useful for something else:

(keymap-set company-active-map "C-M-g" 'company-abort)
(keymap-set company-mode-map "C-M-g" 'company-abort)
(keymap-set company-mode-map "C-<return>" 'company-abort)
(keymap-set company-active-map "C-<return>" 'company-abort)