Can you give your /e/OS version and your phone? See also [HOWTO] Give complete /e/OS version info easily for support, answers, comparison etc
Interestingly, I seem to have aptX on my OnePlus 6 (enchilada) with /e/OS 14, Version 3.0.4. The codec is at least shown in the Bluetooth and the developer settings when I connect my headphones to the smartphone.