Calendar 30 minutes setting for appointments are gone?

Hi. I had a reset of my nextcloud. Since, I cannot enter 30 minutes appointments anymore in my calender. I looked at the settings, the calendar is - as before - on a 30 minute scale. The smallest entry I can make is 1h, that is too big for me. Setting the calendar to 15 minutes scale doesn’t change anything there. Thank you so much for your reply, I really need this feature to organize my day.