Help: Document IOS_INSTALL_COMBINED as deprecated

The approach has not made sense since the introduction of Apple Silicon
and macOS arm64.

Issue: #24957

Help/prop_tgt/IOS_INSTALL_COMBINED.rst

@@ -2,18 +2,27 @@ IOS_INSTALL_COMBINED
 --------------------
 
 .. versionadded:: 3.5
+.. deprecated:: 3.28
+
+  :prop_tgt:`IOS_INSTALL_COMBINED` was designed to make universal binaries
+  containing iOS/arm* device code paired with iOS Simulator/x86_64 code
+  (or similar for other Apple embedded platforms). Universal binaries can only
+  differentiate code based on CPU type, so this only made sense before the
+  days of arm64 macOS machines (i.e. iOS Simulator/arm64). Apple now
+  recommends xcframeworks, which contain multiple binaries for different
+  platforms, for this use case.
 
 Build a combined (device and simulator) target when installing.
 
-When this property is set to set to false (which is the default) then it will
+When this property is set to false, which is the default, then it will
 either be built with the device SDK or the simulator SDK depending on the SDK
 set. But if this property is set to true then the target will at install time
-also be built for the corresponding SDK and combined into one library.
+also be built for the other SDK and combined into one library.
 
 .. note::
 
-  If a selected architecture is available for both: device SDK and simulator
+  If a selected architecture is available for both device SDK and simulator
   SDK it will be built for the SDK selected by :variable:`CMAKE_OSX_SYSROOT`
-  and removed from the corresponding SDK.
+  and removed from the other SDK.
 
 This feature requires at least Xcode version 6.

Help/release/dev/deprecate-install-combined.rst

@@ -0,0 +1,6 @@
+deprecate-install-combined
+--------------------------
+
+* The :prop_tgt:`IOS_INSTALL_COMBINED` target property and corresponding
+  :variable:`CMAKE_IOS_INSTALL_COMBINED` variable have been deprecated.
+  Their functionality does not make sense on Apple Silicon hosts.

Help/variable/CMAKE_IOS_INSTALL_COMBINED.rst

@@ -2,6 +2,9 @@ CMAKE_IOS_INSTALL_COMBINED
 --------------------------
 
 .. versionadded:: 3.5
+.. deprecated:: 3.28
+
+  This is deprecated because :prop_tgt:`IOS_INSTALL_COMBINED` is deprecated.
 
 Default value for :prop_tgt:`IOS_INSTALL_COMBINED` of targets.