QuickLook regression in GHC 9.12

The following program is accepted by GHC 9.10 and rejected by GHC 9.12.

{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE GADTs #-}

module T26030 where

import Data.Kind

type S :: Type -> Type
data S a where
  S1 :: S Bool
  S2 :: S Char

type F :: Type -> Type
type family F a where
  F Bool = Bool
  F Char = Char

foo :: forall a. S a -> IO (F a)
foo sa1 = do
  () <- return ()
  case sa1 of
    S1 -> return $ False
    S2 -> return 'x'

The program is accepted with any of the following changes:

1. Remove the $ in return $ False,
2. Add a certain type signature: return $ ( False :: F a )
3. Remove the () <- return () line.