The only app I miss from Android is BirthDayDroid. This app takes birthdays information from contacts and send notifications about them. Also provides convenient interface too look at the upcoming birthdays. GNU/Linux phones also have contacts and also support birthday fields. But is there a similar app to notify about birthdays?
NextCloud and CalDav is for synchronization, but I use only a single phone, so my contacts are up to date. But what calendar app would you recommend. I currently using Calindori, but it does not support importing events from phonebook as far as I know.
NextCloud automatically creates the birthday calendar based on Contacts information. So NextCloud imports the events, on the backend.
Any calendar that has alerts should work.