I skimmed the article, but what makes Android not sufficient to interact with Muse? I haven’t tried Muse, but I’ve thought plenty about building a local-first notebook app for thinking. Something about pen input or UI jank? Muse seems less general than I was thinking of it as being if only Apple hardware can run its core feature set…
In a word, latency. Everything feeling responsive and tactile is a part of the (tablet part) of the Muse experience. You can see the latency tests for various tablets in a table partway through the essay, and compare those to the human factors research and see that they are off by an order of magnitude for what's necessary to feel responsive. But those tests were a few years ago, would not be surprised if things have improved since then.
TBH I'm not really thrilled about being locked into iPad+Pencil either. But so far, Apple is the only one that has been able to cross the latency threshold with their hardware and OS. Hoping that will not be the case forever.