I can never follow Reddit threads, they’re all over the place.
Running - basically, 5 years after the snap, the Avengers figure out how to time travel (via quantum realm from Antman, and Bruce Banner/Tony Stark being very clever), and they split into teams to pull off a ‘time heist’ and collect all the infinity stones from the past and bring them to the present, where they make their own version of the gauntlet and install the stones. Hulk puts it on and does a snap to bring everyone back, which injures Hulk but he’s ok because Hulk.
But Thanos turns up, big battle with everyone, ending with Iron Man wearing the gauntlet and doing a snap to dust team Thanos, but because he’s only a puny human, he’s fatally injured when he does that and dies on the battlefield with Rhodes, Peter Parker and Pepper all by his side.
Black Widow dies during one of the time heist missions getting the soul stone - same as Gamora did in Infinity War - a soul for a soul. Her and Hawkeye fought over who would sacrifice themselves.
Guardians - Rocket and Nebula afe part of the Avengers team through the whole film, Groot, Quill, Drax and Mantis turn up for the battle. They also have a fun postscript at the end setting up for Guardians 3.
Stan Lee has his final cameo - driving past in the 70s time travel bit, shouting “Make love not war!”