Hi Winmor Tang,
I understand your Bluetooth speaker connects to Windows 11, but the audio is delayed.
Does this happen in every app, and does the speaker work normally with another phone or computer? Please also share the speaker model, PC model, and Windows build shown by winver. It would help to know whether the built-in speakers or wired headphones have the same delay.
For now, remove and pair the speaker again under Settings > Bluetooth & devices > Devices. Then check its sound properties and select 2 channels, 16-bit, 48000 Hz (DVD Quality) if that option is available. If the delay remains, run the Bluetooth troubleshooter in Get Help and install the latest Bluetooth driver from the PC manufacturer.
Let me know the results and I’ll help narrow down the next step.