I have got a QC 35 II and a Huawei mate 20 phone, the buttons on the headphone cannot control the sound of the phone, and the panel of sound control did not poped up. The phone cannot control the volume of the headphone either.
Many thanks for your post and welcome to the community. I am sorry to hear you're having this issue.
May I ask, have you tired the following troubleshooting steps? -
If after doing the above this does not resolve the issue, please let us know and we can assist you further.
Leon_C - Community Support
I'm sorry to hear that troubleshooting hasn't resolved the issue. Have you attempted resetting the phone? This can be done by powering the device down, leaving it to rest for 60 seconds, then powering it back on again to test for results. It may also be beneficial to test pairing a different set of headphones, Bose branded or third-party, to test for volume adjustment control feedback on your Huawei phone. As this problem is isolated to your Huawei Mate 20 Pro, I encourage you reach out directly to them for further technical assistance.