For an example of displaying 3D Tiles in MapLibre GL JS 5.21.1 see
It shows a combination of Mapterhorn terrain tiles, OpenfreeMap vector tiles and 3D Tiles of Dutch buildings.
For rendering the libraries Three.js and 3d-tiles-renderer + plugins are used (like GLTFExtensionsPlugin for EXT_structural_metadata / EXT_mesh_features support and ImplicitTilingPlugin).
Fun part is that people can add their own plugins, for example CESIUM_primitive_outline plugin GitHub - bertt/3dtilesrenderer-outline-plugin · GitHub
Demo: Sibbe 3D Panden
Another one is adding styling language: GitHub - bertt/3dtilesrenderer-styling-plugin · GitHub
Demo: Sibbe 3D Panden
