The Loki TV show goes way deeper into the mechanics of MCU time travel. Basically every timeline where they changed the past is supposed to create an alternate timeline that then gets pruned by the TVA, at least until the end of Loki Season 2 where they switch to a full “it’s a multiverse, infinite alternate timelines are A-OK” stance.

Still doesn’t explain old man Steve Rogers unless he switched timelines to say goodbye to Sam.