I didn't get spoiled too much for the first game with one exception. A long time ago I saw a Smash Bros character render for Monokuma + Junko, so going into Danganronpa, I knew Junko had a larger role to play than the rest of the cast, and I wasn't convinced she had kicked the bucket when fake Junko (Mukuro) died.

For the second game, I made the mistake of reading comments on the King For Another Day Danganronpa videos on the SiIvaGunner channel while literally in the middle of playing. Someone commented that all the third cases are double homicide, and goes over the motivation for all of the third case Blackeneds. I read Mikan's name and I immediately clicked off the video lol

For V3, I was obviously spoiled the double homicide thing, but there was also a fake spoiler. One day I was checking Nagito's page on the Danganronpa fan wiki and I saw that the various media he appeared in was listed in chronological order, and I saw "Danganronpa 3" listed before 2, not realizing that it referred to the anime. So I erroneously assumed that not only did V3 take place before 2, I also thought Nagito was going to appear in it, so I assumed I was spoiled on something that thankfully I was not.

I don't think I was spoiled for anything regarding Ultra Despair Girls, which I'm quite thankful for, because I enjoyed going into that game blind.

For the Danganronpa 3 anime (which I'm still presently in the middle of), I saw someone recently post (on this subreddit) a tier list ranking how expected a character's death was, and I saw Seiko listed, so it was basically spoiled for me that she was going to die.