Most likely, something went wrong with your installation - perhaps settings left over from a previous version. See the Handbook under "Revert to factory settings". If that does not fix the problem, please ask for help diagnosing the problem on the Support forum (Help / Ask for Help from within MuseScore), and provide as much information as you can that might help - what OS you are on, what soundfont you see loaded in View / Synthesizer, what options you see set in Edit / Preferences / I/O.
Comments
Most likely, something went wrong with your installation - perhaps settings left over from a previous version. See the Handbook under "Revert to factory settings". If that does not fix the problem, please ask for help diagnosing the problem on the Support forum (Help / Ask for Help from within MuseScore), and provide as much information as you can that might help - what OS you are on, what soundfont you see loaded in View / Synthesizer, what options you see set in Edit / Preferences / I/O.