Try this: in the Meta Quest Link app on your PC, click your device and under AUDIO, select "use Windows Settings" as the audio source. In your Windows->-System->Sound output source set to your desktop speakers. I think that should work.
Alternatively, I use a free Windows software called VoiceMeeter Banana advanced mixer. It basically creates up to three virtual audio channels. I have mine configured so that the Windows->System->Sound output is "Voicemeeter AUX". Then in the Voicemeeter app on my PC, I have HARDWARE OUT A1 channel set to my desktop speakers using the WDM driver (I have a subwoofer amp connected to the subwoofer output on my PC's sound card, which is connected to a transducer that I bolted underneath my computer chair. That way, it makes my chair shake during explosions and stuff when I am playing games!) - I use this in combination with my Quest 3 for playing seated VR games, or in combination with my bluetooth headset for playing regular 2D games on my PC monitor. To achieve this, I have HARDWARE OUT A2 channel set to "MME: Headphones (Oculus Virtual Audio)" - this sends the Windows audio simultaneously to my Quest 3 (note that it is important to choose the MME driver rather than the WDM driver for the Quest 3 headset audio). Also, I have HARDWARE OUT A3 channel set to "WDM: Headset Earphone" so I can also simultaneously use my bluetooth headset without needing to change any audio settings.