I really hope not. Grampa Roger's being in the main timeline at the end of End Game, suggests that he always was in the timenline, his personal timeline was a "mobius strip". And therefore, a post endgame Steve Rodgers was also active feom past to present in the shadows of the main mcu timeline, working under a different persona.

The best why to explain for these characters suddenly appearing in the main mcu timeline as variants of themselves, is the incursion (that was presented at the end Dr. Strange 2) brought on by the fact the "anchor being" of the main MCU timeline (Tony Stark) had died (a concept presented in Deadpool & Wolverine). This causes the main MCU timeline to collide and merge with another timeline which has an anchor being who is the stark variant that became Dr. Doom since they share the same temporal aura (a concept presented in loki s1e1).

Marvel has laid the ground work for this explanation, and it would truly be a shame if they forgot their own timetravel rules presented in endgame, and changed the way endgame was recieved but suggesting grampa Rodgers ended up in a different branched timeline which would ultimately have broken the tva rules that had not yet been changed (confirmed in loki s1e1 by Judge Renslayer).