The 20 A rating and 6 kA Icn (per EN/IEC 60898-1) cover standard domestic or light commercial final subcircuits at 230 V AC 50 Hz.
Breaking capacity is the headline check: the A9TPD4620 carries three figures. The 6 kA Icn at 230 V AC (EN/IEC 60898-1) is the rated short-circuit capacity for a domestic MCB — enough for most residential boards. The 10 kA Icu (EN/IEC 60947-2) is the industrial rating, covering higher fault-current panels. The 3 kA Icn1 is a lower conditional rating; ignore it unless the supply impedance is unusually high. The limitation class 3 means it lets through very little let-through energy (I²t) on a fault — helps with downstream selectivity and reduces arc-flash risk at the panel.