Der, die or das?
feminine noun · opening ceremony · level A2
die Eröffnungsfeiern - in the plural, every German noun takes the article die.
"Eröffnungsfeier" doesn't follow any of the 35 gender rules - it belongs to the words you learn together with their article, as one unit: die Eröffnungsfeier. That's exactly what the app's spaced repetition is for.