why isn't the events tab activated?

Hello @fuzûlî27 the Events are missing from your game due to an ongoing issue that is explained in the thread linked below

https://community.king.com/en/candy-crush-saga/discussion/427968/%EF%B8%8F-disappearing-events-missing-daily-booster-machine-%EF%B8%8F/p1

Just play a level and your Events should reappear. Please note that this doesn't fix the issue and you will find that you will have to play a level to get your Events to reappear another day as well