[griffzhowl]

Two main reactions:

The Meta paper, as well as other studies which have been interpreted as rudimentary "mind-reading" have measured activity in sensory cortex correlated with direct sensory inputs. There's a fairly close mapping between the initial layers of sensory cortex and patterns of activation in the sense organs. e.g. the optic nerve from each eye projects onto the initial layer of visual cortex in a way that closely preserves the geometry of the retinal image, so it's not that difficult to correlate information in the stimulus and these parts of cortex. Making sense of activity in deeper areas of cortex which isn't as closely correlated with immediate sensory stimulation is a much harder task.

Secondly, the idea seems to be that the brain could make use of a "lossy image" of its own overall functioning. This part seemed very handwavy to me. The brain already contains the information about its own functioning, by definition, so it's not clear to me what functions would be served by the brain's being able to "sense its own magnetic field". It's known that the brain integrates information from distant regions through the patterns of neuronal connectivity. It's not clear that something similar can be done with magnetic fields, because these would mostly affect very nearby areas of the brain, and long-distance effects would be scrambled with all the other activity going on in other parts of the brain.

The idea to look at the effects of the electromagnetic fields in brain functioning is interesting though. The general idea has been around for a long time[0]. The dificult part is making a detailed proposal for how it would actually work and finding experimental evidence for that.

[0] Burr, Northrop (1935) The Electro-Dynamic Theory of Life

https://www.journals.uchicago.edu/doi/abs/10.1086/394488