Configure hidutil to remap Right Fn to act as Right Alt

com.example.KeyRemapping.plist

<!--
  Put this file in ~/Library/LaunchAgents/com.example.KeyRemapping.plist to
  automatically remap your keys when macOS starts.
  See https://developer.apple.com/library/archive/technotes/tn2450/_index.html for
  the key "usage IDs". Take the usage ID and add 0x700000000 to it before putting it
  into a source or destination (HIDKeyboardModifierMappingSrc and
  HIDKeyboardModifierMappingDst respectively).
-->
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>Label</key>
    <string>com.example.KeyRemapping</string>
    <key>ProgramArguments</key>
    <array>
        <string>/usr/bin/hidutil</string>
        <string>property</string>
        <string>--set</string>
        <string>{"UserKeyMapping":[
          {
            "HIDKeyboardModifierMappingSrc": 0xFF00000003,
            "HIDKeyboardModifierMappingDst": 0x7000000E6
         }
        ]}</string>
    </array>
    <key>RunAtLoad</key>
    <true/>
</dict>
</plist>