Are the program Audio/MIDI, ASIO settings (red) are shown as below:
and using the Advanced option (blue) your sound card is set up similar to this.
If these are set as above then we need more information about what you are not hearing sound from ie Soundpools, Instruments or recording from external source.
Also please note there are some bugs in Music Maker 2021 which may affect you - see this bug list
No sound from MM64...the sample song, the soundpools, the instruments...no sound output at all. All other programs on my pc have sound. It seems like I had this problem with the last version of MM as well, but I can't remember the fix. Attached is an image of the audio properties. Really getting discouraged here!!!
What is shown if you click on the "Advanced" button which @johnebaker highlighted? You need to make sure your soundcard/audio interface is selected there, even if it is a built-in one.