3800x is still a very solid CPU.
This PC is probably already closer to being CPU bottlenecked. Meaning the CPU is held back by the GPU. (which is a good thing as it means you're getting the most out of the GPU)
By upgrading your GPU you could double your frames in some games as the 5600xt is a little on the lower end these days. Whereas upgrading your CPU would only give you a few more frames in most cases as it would still be held back by the GPU.
All in all, if you can find one, the 3070 is a good choice for an upgrade.