Gluten-free alternatives to beurre manie/roux for thickening sauce

There's a great overview of the differences here, including a taste-test experiment at the end.

Broadly: beurre manié started off as a "lazy" roux; some people claim that the cooking of the roux reduces any "floury" taste; the experiment did not find any discernible difference between the two options for either a bechamel sauce or a velouté.

I have used quinoa flour in various recipe and it would have a similar effect as the brown rice flour, though its taste would differ. I would recommend against substituting it (at least not 1:1) for the tapioca flour as that is likely working as a kind of binding agent to some extent. Experimentation may yield different results based on the ratio, but also tapioca has less flavor (which may be ideal as a balance).