Timeline.

13 Nov - Ronaldo gets red card in Portugal’s game v ireland. (Should miss opening 2 games of World Cup.)

18 Nov - Ronaldo meets Donald Trump at White House.

25 Nov - FIFA clears Ronaldo to play in World Cup from start.
With a follow-up tweet:
Had a call from a senior football official and his view on this ruling by FIFA to ensure Ronaldo gets to play at the World Cup: “Unprecedented.”Was a different precedent last year when somehow qualification rules emerged to ensure FIFA’s Club World Cup had a Lionel Messi team in it.
That's all from Tariq Panja, a NYT sportswriter. The inference, which probably has at least some merit, is that Ronaldo being a Trump supporter with Infantino earned him special privileges.