EU decided that 2/3 of schedule is enough to hold slots:
EU Decides to Extend Slot Waiver for Summer 2022
More flexibility for take-off and landing rights in 2022
The EU Commission continues to give airlines more flexibility in takeoff and landing rights in the 2022 summer flight schedule. This means that Airlines will have to use 64% of their slots in order not to lose them. In the current winter schedule, the slot waiver stands at 50%. Before the COVID pandemic, airlines had to use 80% of their slots.
The aviation sector is still far from recovered. The development of new virus variants and the resulting travel restrictions means that the situation remains volatile, so these exceptional rulings remain necessary. Without these crisis-related flexibilities, airlines would be forced to fly empty planes to secure their slots.