That's a surprise. The cancer wasn't publicized. He was active at the 50th anniversary less than 2 years ago. I've seen videos of interviews from then, plus when he tried to speak up when Aldrin got all the Buzz with Trump at the podium. Maybe someday I'll type my story. I had to punch someone in the jaw to watch Apollo 11 land. I knew it would the most important event of my life, more significant than any forgettable war.
Not forgotten. Harlan Ellison speculated what would have happened had Collins flown back to Earth, leaving the other two behind on the moon. Sure enough, someone wrote a science fiction story about exactly that.
Collins was the 4th spacewalker, and the 1st to go outside twice in the same mission. I remember every EVA as a semi-failure until slow-moving, slow-breathing Buzz Aldrin kept his faceplate defogged in Gemini 12. So NASA invented bulky water-cooled Apollo spacesuits. https://en.wikipedia.org/wiki/List_of_spacewalks_and_moonwalks_1965–1999#1965–1969_spacewalks_and_moonwalks
Back in 1990 I attended a conference where Neil Armstrong spoke, it was and ok speech. Even he admitted it wasn't his favorite thing to do. He got very serious about halfway through and talked about the depression he suffered once back and how it was very tough to embrace reality and little things. It took him a while to feel whole again and that there was much more to life, he said. he commented that he felt empty for some time. Then he shifted gears and talked about the space program i general and why its important to explore not only in space but here on mother earth.
He didnt really get into it, that I recall. Made comments about budgets and engineering and Space Shuttle efforts. Also mentioned those that gave their lives.
Buzz Aldrin became an alcoholic for a few years after Apollo 11. Armstrong became a professor and should have become proficient at public speaking.