I reckon most people would say Ronaldo's iconic season in the CL was in 16-17, when he scored 5 against Bayern in the quarters, a hat-trick against Juve in the semis, and a double against Atletí in the final. He scored just 2 goals in the group stages then, just as he has this season. And last season he scored 5 goals in 4 games in the knockout stages, including the hat-trick to singlehandedly knockout Atletí, while only scoring 1 goal in the group stages. Ronaldo has been much more decisive in big games in his 30s than he ever was in his 20s, and there's been no sign of that fading yet.