Anyway at some point one of Rheem's other customers got pissed off enough with this tragicomedy to just completely write their own software from scratch, and of COURSE it works way better than the dogshit that Rheem put out
So yeah, the solution is to install Home Assistant on and old Raspberry Pi, get an ESP32 module and some phone wire, plug into the diagnostic port on the front and bypass everything to do with the official app and wifi interface entirely in favour of one that works.
Unfortunately this means you now have Home Assistant in your home, which means you now have a new hobby whether you want it or not