Did you enable developer mode and go into your developer options settings to see if the codec was available? AptX and aptX HD seem to be compatible with most of the newer Pixel phones including Pixel 9, so you might just need to go into your dev options to enable it. I personally have been trying to set my codec to Aptx HD for my Pixel 7 with my XM3s in the settings but after I do it, the codec returns back to LDAC once my phone reboots, so I don't know if that method really works for sure or if it's an issue with compatibility. But just wanted to let you know that could be something to try to see if it's already an option