The System.IO.Seek module is redundant from ghc-8.10.7 onwards.

README.md

@@ -1,4 +1,6 @@
 [![Haskell CI](https://img.shields.io/github/actions/workflow/status/input-output-hk/fs-sim/haskell.yml?label=Build&style=for-the-badge)](https://github.com/input-output-hk/fs-sim/actions/workflows/haskell.yml)
 [![handbook](https://img.shields.io/badge/policy-Cardano%20Engineering%20Handbook-informational?style=for-the-badge)](https://input-output-hk.github.io/cardano-engineering-handbook)
 
-# fs-sim
+# fs-sim
+
+`fs-sim` and `fs-api` are unlikely to work with GHC versions before `ghc-8.10.7`. See the `tested-with` fields in [`fs-api.cabal`](./fs-api/fs-api.cabal) and [`fs-sim.cabal`](./fs-sim/fs-sim.cabal) for the GHC versions that we test with.

fs-api/fs-api.cabal

@@ -42,12 +42,6 @@ library
                     , Util.CallStack
                     , Util.Condense
 
-  if os(windows)
-    exposed-modules:
-                      -- TODO Delete this module once all our projects have upgraded to at least
-                      -- ghc-8.10.7, but not before
-                      System.IO.Seek
-
   default-language:   Haskell2010
 
   build-depends:      base        >=4.14  && <4.17

fs-api/src-win32/System/IO/FS.hs

@@ -20,14 +20,10 @@ import           Data.ByteString
 import           Data.ByteString.Internal as Internal
 import           Data.Word (Word32, Word64, Word8)
 import           Foreign (Int64, Ptr)
-
--- Dodgy import when Win32 >= 2.6.2.0
-import           System.Win32 hiding (setFilePointerEx)
-
 import           System.FS.API.Types (AllowExisting (..), FsError (..),
                      FsErrorType (..), OpenMode (..), SeekMode (..))
 import           System.FS.Handle
-import           System.IO.Seek (setFilePointerEx)
+import           System.Win32
 
 type FHandle = HandleOS HANDLE