I found this repo early on and have been using it to run inference on my M1 Pro MBP. https://github.com/ModeratePrawn/stable-diffusion-cpu

For me it runs at about 3.5 seconds per iteration per picture at 512x512.

There is also a fork that uses metal here and is much faster: https://github.com/magnusviri/stable-diffusion/tree/apple-si... but it doesn't support seeding the rng and will occasionally produce completely black output. Useful if you want to spit out a whole bunch of images for one prompt but you lose the ability to re-run a specific seed with a tweaked prompt or increased iterations.