RequiredTypeArguments: unexpected parse error for infix type

I am using GHC 9.10.1-alpha1, which introduces the RequiredTypeArguments extension. My understanding is that a visible forall can be instantiated with a type (without needing a type disambiguator) when the name of the type is unambiguously in the type syntax. For example, the following works as I would expect, since (:!@#) is unambiguously in the type syntax:

{-# LANGUAGE GHC2024 #-}
{-# LANGUAGE RequiredTypeArguments #-}
module Foo where

import Language.Haskell.TH

idee :: forall a -> a -> a
idee _ x = x

type (:!@#) = Bool

f :: Bool -> Bool
f = idee (:!@#) -- Relies on RequiredTypeArguments to work

So far, so good. Now consider what happens if we change the name of the type slightly:

-- No longer starts with a colon
type (!@#) = Bool

f :: Bool -> Bool
f = idee (!@#)

The name has changed to (!@#), but it's still unambiguously in the type syntax. Despite this, GHC no longer accepts the program!

$ ghc-9.10 Foo.hs
[1 of 1] Compiling Foo              ( Foo.hs, Foo.o )

Foo.hs:14:5: error: [GHC-76037]
    • Not in scope: ‘!@#’
    • In the expression: idee (!@#)
      In an equation for ‘f’: f = idee (!@#)
   |
14 | f = idee (!@#)
   |     ^^^^^^^^^^

This error message is very surprising, as (!@#) is in scope. Surely this ought to be accepted? At the very least, I didn't see this limitation of RequiredTypeArguments mentioned in the relevant section of the GHC User's Guide.