what is more important for performance in Unity.
Do we need to put effort on reducing vertices count or uv count.
You want to minimize the number of vertices that the GPU has to process. However, you need to understand that to the GPU a “vertex” is a unique combination of position, normal, uv, and other things like color, tangent, etc. Every UV seam, hardened normal edge, color discontinuity, etc can all create multiple vertices at the same position. To cut down on the number of vertices, you can remove entire vertices or you can cut down on the number of discontinuities (i.e. seams) in normals, UVs, etc. What solution is best depends entirely on your content.
Also, it’s worth noting that GPUs are actually pretty darn good at processing vertices, even mobile GPUs. Most games are more CPU bound than GPU bound and when they are GPU bound it tends to be in pixel processing more than vertex processing (there are many pixels for every vertex in most games). Make sure that you always optimize based on profiling, not just what you think or have heard is slow.