For anyone else reading this, librera reader + sherpaTTS are both FOSS android apps and can read anything librera can open on an ad-hoc basis, with no need to futz with files, just load your ebook bookmark and hit play.

SherpaTTS has a bunch of different models (piper/coqui) with a ton of voices/languages. There's a slight but tolerable delay with piper high models but low is realtime.