Yes, you can stack a circular polarizer on a UV filter, but there are tradeoffs.

Main downsides:

• mechanical vignetting: the extra filter ring can darken corners, especially on wide-angle lenses; it’s less likely on longer focal lengths or some crop-sensor setups
• more flare/ghosting: each filter adds glass-air surfaces, increasing reflections, especially when shooting toward bright light
• lower contrast: for the same reason, stray reflections can reduce image clarity
• extra light loss: a UV filter absorbs a little light, and a polarizer absorbs much more
• filters can seize together if tightened too much

In practice, stacking may be acceptable in some situations, but it is usually not ideal for best image quality. If you do it, test your lens at the widest focal length and check the corners for shading. Also avoid overtightening the filters.

If you want the cleanest results, remove the UV filter before using the polarizer.