Upgrading to the Ryzen 7 5700X3D would likely provide a significant performance boost, especially in CPU-heavy tasks and gaming, due to its additional cache and architectural improvements compared to the Intel i3 12th gen. However, if you're planning a GPU upgrade soon, the performance improvement might be bottlenecked by your current RX 6600, so the overall impact on gaming might be limited until you upgrade the GPU.
For alternatives in a similar price range, you could also consider other Ryzen 5 or Ryzen 7 models or Intel's 12th gen i5 or i7 processors, depending on availability and pricing. If you're future-proofing for a more powerful GPU, the Ryzen 7 5700X3D would be a solid choice, as it should pair well with high-end GPUs.