Hi Dávid Majlát
Welcome to Microsoft Community.
I understand that you are having trouble after updating Windows 11, when using discord voice other people can hear the sound playing on your computer, I know exactly how you feel, please let's work together to solve this problem!
I'm going to give you some things to check as well as a solution that will hopefully solve your problem successfully.
Option 1: Please try to record your voice through the built-in function of Discord while using Discord Voice, and then listen to see if you can hear the sound playing on your device. Please also check if Discord has an audio source and other relevant settings and set it to microphone.
Option2: Please try using other voice software, such as Team Speaker, to see if the same problem occurs.
Option3: Please uninstall the last update of Windows 11 and wait for the next update to synchronize the update.
“Windows Logo Key + i” to open “Settings” -> Find “Windows Update” -> Click “Update history” -> Click “Uninstall updates” -> Find your latest installed update and click “Uninstall” on the right side
After uninstalling, please try using voice software to see if the same problem occurs.
I sincerely hope that the above solution will solve your problem.
We look forward to hearing back from you.
Best Regards
Arthur Sheng | Microsoft Community Support Specialist