Same issue here - trial user with HomePod Mini stereo pair.
The 2 HomePod Mini's are paired, upgraded to newest version 26/10 (15.x) and work fine with Apple devices (iPhone, iPad, MacOS 12) but not with TuneBlade.
TuneBlade are seeing the devices as single and not paired. Streaming to a single one appears to fine stable and well from any tested application source.
However, streaming to both (as single devices fail spectacularly) - they keep dropping connecting back and forth between the devices - a real mess - and pity.
I have 5 more HomePod Mini's coming my way and was hoping to be able to use a new stereo pair with Win10, so hope it gets fixed.
Once fixed, I'll definitely be getting a license - this software fills a much needed empty space left by Apple - and Apple will never fill it, so hope the developer keeps up on the development.