Starting from Zemo in the first whose influence rose after his possible escape soon as the Blip came to pass.

Leading then to personal conflict against Sharon, now Powerbroker & then ending on Red Skull whose fate was left open since his obligation on Vormir ended as the stonekeeper which Russo Brothers also discussed shortly after Infinity War's release.
Had Sam received his proper trilogy as Captain America, these would have fit as antagonists in each film.