Its interrupting capacity reaches 121 kA at 240 V, 75.6 kA at 415 V, and 52.5 kA at 440 V — figures that tell you the fault energy this thing can clear without venting the panel. That 121 kA at 240 V is the headline number for most industrial distribution boards; the 75.6 kA at 415 V covers the common European 400 V three-phase bus.
The breaker holds its full 63 A rating up to 50 °C ambient, then derates to 60.48 A at 55 °C, 59.22 A at 60 °C, 57.96 A at 65 °C, and 56.7 A at 70 °C. If your enclosure runs hot — near a furnace line or a bank of drives — that derating curve is what you size the feeder for, not the 63 A nameplate.