+What Happened+
Using the BasicImageTracking scene from Samples with the museum Simulation Environment, upon entering Play mode for AR Sim the error below appears in Console.

+Configuration+
2021.3.0f1.2 (2021.3/staging 6eacc8284459)
MacOS 12.0.1, MacBook Pro (15-inch, 2019), 2.4 GHz 8-Core Intel Core i9
AR Foundation 5.0.0-pre.10 (0a49b4f)

+Error+
ArgumentException: The number of vertices in the combined mesh (101437) exceeds the maximum supported vertex count (65535) of the UInt16 index format. Consider using the UInt32 IndexFormat for the combined mesh to increase the max vertex count.
UnityEngine.Mesh.CombineMeshes (UnityEngine.CombineInstance[] combine) (at /Users/bokken/buildslave/unity/build/Runtime/Export/Graphics/Mesh.cs:1336)
UnityEngine.XR.Simulation.SimulationMeshSubsystem.CreateMeshFromCombineList (System.Collections.Generic.List`1[T] combineInstancesList, UnityEngine.Rendering.IndexFormat meshIndexFormat) (at Library/PackageCache/com.unity.xr.arfoundation@5.0.0-pre.10/Runtime/Simulation/Subsystems/Meshing/SimulationMeshSubsystem.cs:227)
UnityEngine.XR.Simulation.SimulationMeshSubsystem.AddMeshesWithClassification (System.Collections.Generic.List`1[T] meshFilters, UnityEngine.Matrix4x4 environmentWorldToLocal, System.String classification, UnityEngine.XR.Simulation.MeshDiscoveryParams meshingSettings) (at Library/PackageCache/com.unity.xr.arfoundation@5.0.0-pre.10/Runtime/Simulation/Subsystems/Meshing/SimulationMeshSubsystem.cs:200)
UnityEngine.XR.Simulation.SimulationMeshSubsystem.AddMeshes (UnityEngine.GameObject environmentRoot) (at Library/PackageCache/com.unity.xr.arfoundation@5.0.0-pre.10/Runtime/Simulation/Subsystems/Meshing/SimulationMeshSubsystem.cs:172)
UnityEngine.XR.Simulation.SimulationMeshSubsystem+<>c__DisplayClass11_0.<OnEnvironmentReady>b__0 () (at Library/PackageCache/com.unity.xr.arfoundation@5.0.0-pre.10/Runtime/Simulation/Subsystems/Meshing/SimulationMeshSubsystem.cs:135)
UnityEditor.EditorApplication.Internal_CallDelayFunctions () (at /Users/bokken/buildslave/unity/build/Editor/Mono/EditorApplication.cs:371)