hi, I also use the Fiio BTR3.
However, the HWA / LHDC codec, but the Fiio BTR3 plays Hi-Res audio with a maximum of 24 bit and 96 kHz.
Can you access the developer settings of your phone?
There you can make the Bluetooth audio settings like sample rate, bit depth, codec, audio quality and latency.
You can also download the Fiio Music app, the settings that you keep there are stored on the BTR3.