It falls in the Peter Parker goes on a field trip trope. But it takes place after Endgame, where Tony is dead.
There is some sort of memorial service taking place at SI for Tony and Peter's class is invited for an extended period of time. Peter doesn't want to go, but I think Pepper and May insisted.
Anyway, what I remember most is that Peter uses his old physical badge from before the snap, which no one has seen in years, and Harley is the tour guide. At one point, Friday pipes up to tell Peter that Tony has a message for him, and Peter basically has a breakdown.
Eventually there is a very emotional tribute everyone takes part in.
I remember reading it on both fanfic.net and AO3, but now I can't find it. If anyone knows it, I'd appreciate any info. Thank you.