I also tried updating my drivers: I installed the MediaTek drivers directly from the Microsoft Update Catalog to test LE Audio:

- MediaTek Bluetooth (radio) — v25.40.2.227 — https://catalog.update.microsoft.com/ScopedViewInline.aspx?updateid=929af3ec-9776-410c-804e-9516704c830e
- MediaTek MEDIA (Bluetooth LE Audio / ACX) — v1.6.0.48 — https://catalog.update.microsoft.com/ScopedViewInline.aspx?updateid=e35e9f70-eb39-48e1-b678-bd8ff3f782ae
- MediaTek MEDIA (Bluetooth LE Audio / ACX) — v1.5.0.46 (also tested)
 

The card works perfectly (even better than with the TP-Link driver) , but MediaTek MEDIA installs without attaching to any device, same problem as before. The radio driver does not create the Bluetooth audio child device, so the ACX component has nothing to bind to and no LE Audio node is exposed, and the "Use LE Audio when available" toggle never appears.

  @Henri86245 

Hi,

Out of interest I tested the Bluetooth driver v25.x you mentioned with my generic MT7922 and you are right, that driver doesn't activate LE Audio.

If you'd like you can try driver version RZ6xx (MT7921/MT79x2) 1.1146.0.576 available for download via this link
https://www.elevenforum.com/t/drivers-amd-mediatek-wifi-bluetooth.11384/
With this driver version (as well as several previous v1.1xxx.x.xxx versions) LE Audio has been working fine with my generic MT7922.

Note that this driver doesn't include TP-Link's custom hardware ID VID_13D3&PID_3610 and so you would need to install it via the "Have Disk" method of the Device Manager. (after you've browsed to the correct mtkbtfilter.inf choose "MediaTek Bluetooth Adapter" from the list)
 

Thanks @woozle,

I tried the RZ6xx 1.1146.0.576 driver via "Have Disk" > "MediaTek Bluetooth Adapter". The radio installs fine (OK under my VID_13D3&PID_3610), but LE Audio still won't bind, even after a scan-for-devices + (reinstall mtkbtacx) + reboot.

Digging into it, the problem is that my PID lands in INF section MTKBT_T0_2, and that section is missing what enables LE Audio

> $id = (Get-PnpDevice -Class Bluetooth | Where-Object { $_.InstanceId -match "VID_13D3&PID_3610&MI_00" } | Select -First 1).InstanceId
> Get-PnpDeviceProperty -InstanceId $id -KeyName "DEVPKEY_Device_DriverInfSection","DEVPKEY_Device_Manufacturer","DEVPKEY_Device_DriverVersion" | Select-Object KeyName, Data

KeyName                         Data
-------                                 ----
DEVPKEY_Device_DriverInfSection MTKBT_T0_2
DEVPKEY_Device_Manufacturer     Mediatek Inc.
DEVPKEY_Device_DriverVersion    1.1146.0.576

Here is what I traced in mtkbtfilter.inf:

1) T0_2 HAS NO CIS OPT-IN (vs T0_3)

> Select-String -Path "BT\mtkbtfilter.inf" -Pattern "\[MTKBT_T0_2\.NTamd64\.HW\]" -Context 0,6

[MTKBT_T0_2.NTamd64.HW]
     needs = BthUsb.NT.HW
     needs = BthLEExtendedAdvertisingOptIn.HW           <- no CIS line
 

> Select-String -Path "BT\mtkbtfilter.inf" -Pattern "\[MTKBT_T0_3\.NTamd64\.HW\]" -Context 0,6
   [MTKBT_T0_3.NTamd64.HW]
     needs = BthUsb.NT.HW
     needs = BthLEExtendedAdvertisingOptIn.HW
     needs = BthLEConnectedIsochronousStreamsOptIn.HW   <- CIS (required for LC3) 
 

2) T0_2 HAS NO .Components / AddComponent (the key one)

> Select-String -Path "BT\mtkbtfilter.inf" -Pattern "AddComponent|Component|acx|IsochronousStreams|LEAudio|LE_Audio"
 

 AddComponent = mtkbtacx exists for T0_3, T0_4, A1_2, A1_3,
   A2_2/3/4, D1_2/3, H1_1, H2_2/3, L1_1, L1_3...
   but there is NO [MTKBT_T0_2...Components] section at all.
 

   [AddComponentSection]
     ComponentIDs = VEN_0E8D&SID_0001     <- exactly the node I never get

Conclusion: for T0_2 the filter never runs AddComponent, so VEN_0E8D&SID_0001 is never created, and the ACX has nothing to bind to (hence "attached to 0 devices"). The silicon clearly supports it: the INF even ships the Parameters\mtkbt LEAudio_SideBand and ACP_Support_LE_Audio reg keys. 


 

Edit:

As a test I forced section MTKBT_T0_3 through the registry. The card works under that section, but because the registry override is ephemeral, AddComponent never runs and the child nodes are never created. 
 

The real fix is on the publisher side: map VID_13D3&PID_3610 to a section with the CIS opt-in + AddComponent block (like T0_3). The module clearly accepts T0_3 and BT keeps working, so it should be a trivial, safe change.

  @Henri86245 

Thanks for digging into this.

To me the conclusion is that this can't be an oversight. Linking "needs = BthLEConnectedIsochronousStreamsOptIn.HW" only to certain hardware IDs, but not to others, clearly must be intentional. 
Who knows? Maybe MediaTek also sells their Wi-Fi+BT modules without the LE Audio feature, upon request? (I mean to bulk customers who order them in large quantities) 

To be fair, TP-Link does not advertise the Archer TX55E as supporting LE Audio.