UIMeshRenderer is a renderer component with a conversion feature that converts 3D models from 3D render pipeline to 2D. This component supports rendering the 3D model and particle system in the UI, without the component, the 3D model and particle system nodes will not be rendered.
The UIMeshRenderer component is added by selecting the node in the Hierarchy panel with the MeshRenderer or classes inherited from it, then clicking the Add Component button below the Inspector panel and selecting UI/Model. And the particles are added to the particle nodes. The usual structure is as below: