If you are looking at your Cupla calendar on an iPhone and there is no + button, it has almost certainly not disappeared — it has moved into the ⋯ menu in the top right corner of the calendar.
Tap the ⋯ in the top right and the + (Add Event) will be in the menu that opens.
Why it moves
iPhone decides how many buttons fit across the top of the calendar. When they do not all fit, it tucks the extra ones into a ⋯ menu rather than shrinking them. Two things commonly trigger this:
iOS 26, which changed how apps pack buttons into the top bar.
A large text size on your phone, which makes each button wider.
The Today button moves into the same menu, so if you have also lost your way back to the current day, look for it there.
Other ways to add an event
You can always add an event from the Home screen instead: tap + in the top right, then Add Event.
Once the event form is open, everything works as usual — see How do I create a shared event or date?
Bringing the + back onto the bar
If you would rather have the + visible on the calendar itself, reducing your phone's text size gives the buttons room to fit again — see How do I adjust the font size?
If the ⋯ will not open
If tapping ⋯ does nothing, fully close Cupla and open it again, and check the App Store for an update. If it still will not open, message our support team from the app and send us a screenshot of your calendar screen — that shows us exactly which buttons your phone is displaying.