Hi @Anonymous ,
The problem with the formula is that the Notify function is only called once for the first employee whose birthday is today.
This is because the ForAll function is used to iterate through all employees, but it does not accumulate the results of the notification function for each employee.
Do you want to display the name of the person whose birthday is today in a reminder?
Please try to display people's names together:

Notify(If(CountRows(Filter(event,Text(Starttime,"mm/dd")=Text(Today(),"mm/dd")))>0,"HB"& Concat(Filter(event,Text(Starttime,"mm/dd")=Text(Today(),"mm/dd")),Title,"And"),"Niemand jarig"),NotificationType.Information)

Here is result:

Best Regards
Cheng Feng