Hi everyone,
Also like @mgt I have a mature expo managed project (started on SDK 31) that is currently running SDK 36 perfectly on both android and ios. Product lifecycle now claims for a web version and while following the setup to integrate the web platform to our expo.platforms array on app.json was seamless (thanks to the great docs! 
), I got this error when compiling it for the web. Please note that it is slightly different from the one that the thread author posted, but follows within the same category:
Failed to compile.
./node_modules/react-native/Libraries/Components/TextInput/TextInputState.js
Module not found: Cannot resolve '../../Utilities/Platform' in './node_modules/react-native/Libraries/Components/TextInput'
Looking into node_modules/react_native folder, I saw that indeed the node_modules/react-native/Libraries/Utilities/Platform.js doesn’t exist, but it has Platform.android.js and Platform.ios.js.
So when I read @wodin suggestion, I tried to spin up a brand new CRNA managed project hoping to see what those node_modules/react-native files looked like on a web build that could successfully compile so I maybe could figure out which react-native/platform file to use (fixed with patch-package or something else), but ended up having another unrelated issue that also has an open thread here at expo forums… 
All help and/or insight into any of these issues would be greatly appreciated. Thanks in advance!