Microphone doesn't work on the website duolingo

I have a problem with my USB microphone. I would like to use this microphone for speaking exercises on the Duolingo website. I gave the permissions for the microphone in the Swiron browser, but when I start with the language exercise, this exercise breaks immediately without making a sound. When I go to the sound option (system properties) and test the output sound, the sound always comes through the loudspeaker and not through the headset. The input sound is properly received via the headset micro. I use Ubuntu Ubuntu 20.04.4 LTS on Acer Aspire V17 Nitro Laptop.

Best Regards, Daniel

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