Record internal sound Does not work?

I want to record sound internally with my laptop (Windows 10), but it does not work.

I have the program Magix music Cleaning Lab 15 deluxe to record. If I'm in the sound settings and also activated Steromix as a recording device, and deactivated the microphone, it will not work. The level to the right does not bounce when I play a song, for example.

What do I have to do so that I can record internal sound? Or what exactly do I have to set to make everything work?

Try it with OBS Studio. So you can record only the sound with: https://obsproject.com/de

Also try the Apowersoft audio recorder

How do you record only the sound?

For this one must select only with the output format MP3.

That does not work for me.

Try this: https://www.aiseesoft.de/tutorial/pc-sound-aufnehmen.html