Good day to you Lombarlo,
We’d like to have you check to ensure your Birthday calendar is selected, to ensure those show accurately in the Calendar app: Set up multiple calendars on iPhone
To view multiple calendars, tap Calendars at the bottom of the screen, then do any of the following:
• Select the calendars you want to view.
• Tap US Holidays to include national holidays with your events.
• Tap Birthdays to include birthdays from Contacts with your events.
If that isn’t working, please next go to the Contacts app and verify that the birthday for a specific contact shows on their contact card: Edit contacts on iPhone - Apple Support
Thanks.