default Birthday Calendar not visible in iphone

you can try to get your Birthdays calendar to show up in the iPhone Calendar app:

* Enable Birthdays in Calendar Settings:

* Open the Settings app on your iPhone.

* Scroll down and tap on Calendar.

* Under Accounts, tap on the account where your birthdays are stored (e.g., iCloud, Gmail).

* Make sure the Calendars toggle is switched on for Birthdays.

* Turn on Show All Calendars:

* In the Calendar app, tap on Calendars at the bottom of the screen.

* Ensure that the Show All Calendars toggle at the top is switched on.

* Force Quit and Relaunch Calendar App:

* Swipe up from the bottom of the screen (or double-click the Home button on older iPhones) to bring up the App Switcher.

* Swipe up on the Calendar app preview to close it completely.

* Relaunch the Calendar app and see if your Birthdays calendar appears.

If none of these solutions work, you can try restarting your iPhone or deleting and re-adding your account to the Calendar app.