Steps to reproduce:
1. Open attached "testproj.zip" Unity project
2. Switch to Android build target in Build Settings
3. Switch Scripting Backend to IL2CPP (notice how x86 (Chrome OS)" target architecture is automatically enabled)
4. Build for Android in Build Settings

Expected result: Project builds successfully
Actual result: Build fails with error
UnityException: Unable to package apk
Unity library missing for the selected architecture x86 (/Applications/Unity/Hub/Editor/2021.1.17f1/PlaybackEngines/AndroidPlayer/Variations/il2cpp/Release/StaticLibs/x86/libunityruntime.a) !
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr, Boolean&) (at /Users/bokken/buildslave/unity/build/Modules/IMGUI/GUIUtility.cs:189)

Reproduced with: 2021.1.17f1
Didn’t Reproduce with: 2022.1.0a5, 2021.2.0b6, 2021.1.16f1, 2020.3.15f1, 2019.4.29f1

Note: "x86 (Chrome OS)" Target Architecture is enabled by default when this project is upgraded to 2021.1.17f1, meaning some upgraded projects will fail to build on android il2cpp by default

Workaround: Disable "x86 (Chrome OS)" Target Architecture in Project Settings