Hi Amine,
I'm Sumit, here to answer your query at the Microsoft Community.
Apologies for any inconvenience you are experiencing. I am happy to help you today.
When you record the screen, there is an option to record the output and the Mic. Are you sure you enabled the same?
Also, let me know the make and model of the device to help you further.
I look forward to your reply and am ready to collaborate until we reach a resolution. Best of luck!