This is not strictly true. Guidance has been issued that COVID can be deemed extraordinary circumstances, but that does not mean all cancellations can be attributed to COVID. For cancellations in March and April, almost certainly, but flights deliberately scheduled during the pandemic that were then subsequently cancelled at short notice might not be treated this way by courts. As always, it depends on the individual circumstances.

For example, a flight failing to depart on time during the pandemic due to a technical defect cannot be considered to be due to COVID. I expect the Airline would maintain that the engineer supposed to fix the problem took longer due to COVID but I suspect most courts would be unsympathetic to this.

EDIT: In my opinion, the LH Group practice of only cancelling flights at (very) short notice in order to make nervous passengers voluntarily rebook instead of getting refunds may well also fall foul in court when challenged. Especially when one makes the case with evidence that this was systematic.