[ItsMikeE]

I thought OP3 did not have aptX bluetooth

Running stock OxygenOS 4.5.0
Went into Settings, hit search and typed in APTX

Two options came up:
aptX / aptX HD Support
Bluetooth Audio Codec

but when I select them I go to settings screens which do not show those options

So is aptX available? Automatically used with Media Audio when paired with aptX enabled headphones?

[SactoKingsFan]

Official OxygenOS doesn't currently support aptX. I'd expect aptX with Oreo update. If you really want aptX before Oreo you can use OxygenOS open beta, Freedom OS or use the aptX magisk module.

[ItsMikeE]

Strange that it shows up in the settings search

Fingers crossed for inclusion with Oreo

[SactoKingsFan]

Strange that it shows up in the settings search

Fingers crossed for inclusion with Oreo

We now have aptX and aptX HD in codec settings with recently released open beta 19.

[ItsMikeE]

Now with 5.0.1 update it appears in Developer Options / Bluetooth Audio Codec
I tried setting it, but it sets itself back to the default "Use System Selection"

[ItsMikeE]

Found the answer for myself
Switches itself on automatically when it detects that it is connected to aptx compatible headphones