The metronome in Notion will play with the bpm value that you have set for your tempo. Just add a metronome marking to your score and set the desired beats per minute. You can double-click the metronome marking/tempo marking to change the bpm value. If you double-click the tempo marking, you will notice that it is set to Q=90. You can change the q to a e and this will give the eighth note the beat.