$ mkdir temp
$ cd temp
$ cabal --version
cabal-install version 3.6.2.0
compiled using version 3.6.2.0 of the Cabal library
$ cabal init
...
$ cat temp.cabal  # edit temp.cabal so it looks like this:
cabal-version:      3.6
name:               temp
version:            0.1.0.0
extra-source-files: CHANGELOG.md

build-type: Custom
custom-setup
  setup-depends:
      base  ^>= 4.14
    , Cabal ^>= 3.6

executable temp
    main-is:          Main.hs
    build-depends:    base ^>=4.14.3.0
    hs-source-dirs:   app
    default-language: Haskell2010
$ cat Setup.hs  # edit Setup.hs so it looks like this:
module Main (main) where

import Distribution.Simple

main :: IO ()
main = do
  putStrLn "Confirm I'm using Setup.hs"
  defaultMainWithHooks $ simpleUserHooks
    { preClean  = \_ _     -> error "preClean should fail"
    , cleanHook = \_ _ _ _ -> error "clean should fail"
    , postClean = \_ _ _ _ -> error "postClean should fail"
    }
$ cabal v2-build
... # builds correctly; echoes "Confirm I'm using Setup.hs"
$ cabal v2-clean -v
Deleting dist-newstyle (/Users/jsm/workspace/temp/dist-newstyle)