All I can remember is that it took part in the 2012 Avengers alternate timeline from Endgame with the 2012!Steve first thinking that EG!Steve was Loki messing with his head, 2012!Tony found vid evidence of their alternative selves but also alternate Bruce. Also had Hydra!SHIELD agents thinking that 2012!Steve was Hydra because of EG!Steve. Only Tony and Steve know about the alternates and Hydra in SHIELD. Steve decides to go undercover into Hydra with Tony's support i think?
Tony and Steve get together sometime heading towards the end on the fic? I don't think it's a series, could be a one off but I'm kinda worried I may be mixing fic together.
[UPDATE] So the main alternative 2012 story called 'Alternatively' by 16woodsequ. Still have no idea bout the stony part. I think i definitely mixed another story and Alternatively together.