'At first he couldn't hear the voice, he couldn't hear anything. But gradually he became aware of it, coming and going in bursts. He tried to grasp it, hold on to it, but it kept slipping away.
"Bucky? Can you hear me? Can you breathe for me?"'
When there's gaps in the canon, what's fanfic to do but to, y'know, step in...?
Like, when Avengers: Endgame leaves everyone in a nebulous situation, and The Falcon and The Winter Soldier (TFATWS) picks up after all the messy logistical stuff has already been dealt with and the brainwashed supersoldier assassin has already been pardoned.
...None of this is spoiler-y, since you can pretty much assume this from the trailer for TFATWS. #Don'tComeForMe
(Fandom notes:
Canon is the 'official' stuff in the book/film/whatever.)