It's hard to critique this paper directly because its claims are so incoherent and decorated with so much obnoxious verbiage[1] that people aren't going to believe me when I point out what the claims actually are.
Regardless, this is their paper:
First, they conflate the substrate with the presentation layer. Then, they point out that Turing equivalence means you can run an LLM on anything, with a pointless aside where they nerd out about making a logic gate in AoE II. This lets them conclude that you can use anything as the presentation layer.
Then they claim that it's natural to ascribe human-like attributes to outputs from some presentation layers, like abstract letter symbols on a computer screen, but not to most other things, like patterns of goats on AoE II, or LEGO. Yes, this seems to imply if your partner writes something heartwarming to you using LEGO, you're meant to laugh at them and point out how LEGO isn't intelligent so this isn't evidence of anything.
Then they do a thing where they say that assuming substrate independence is true (or false) prevents proving whether substrate independence is true or false, and from this, but just by vibes AFAICT, make it sound like everything one could learn about attributes of a system from its outputs is circular.
Then they write a bunch more incoherent text and mercifully then it ends.
[1] 'from an epistemic perspective, we argue that a generalised conclusion such as that necessarily requires a well-designed experiment' — the whole thing is like this.