Related question: Can I buy a desktop Zen 5 CPU and something like an RX 7600 XT and some RAM and have a high shared memory bandwidth situation between the system memory and the GPU ala Strix Halo and Apple Silicon without spending a ton of money?

And get pretty reasonable local LLM performance on some of the larger models for hobbyist use?

Edit: I don’t have a good grasp on this but I’m thinking I can only do shared memory when I’m using an APU and not a discrete GPU. Is this correct?

No, memory is not "unified" when you have a physically separate GPU. In that case memory is accessed through the PCIe bus which will be a significant bandwidth bottleneck. PCIe tops out at 64GB/s for 16 lanes of PCIe 5 and not all GPUs support that.