DxO Photolab can process jpegs, and most of the tools and adjustments work on jpegs.
There are some limitations. For denoising, only one method (Standard) is available. For WB, only the Temperature can be changed, from cooler to warmer.
It is understandable that one can do more with raw files, less with jpegs, yet jpegs can be improved by additional processing.
If you have the latest Topaz (in Photo AI or Gigapixel), see if you may like the effect of upscaling (even slight, e.g. by 10%). This involves some denoising and sharpening in addition to increasing the pixel size. There is no guarantee that the result should be to your liking, but might be worth trying anyways.
