An episode pitch involving the Guardians of the Galaxy was suggested for the first season, but it had to be scrapped after A.C. Bradley was told that she had inadvertently written half the plot of Guardians of the Galaxy Vol. 3 (2023).
Uatu was initially conceived as being a cold, stoic observer of the show's alternate realities. After Jeffrey Wright described the experience of watching Marvel movies with his kid however, the character was re-written to have a warmer and more devoted interest in what he was watching instead.
One episode idea that A.C. Bradley came up with would've involved Loki becoming worthy to wield Mjolnir. This idea was discarded early on however, as the idea of Loki becoming a hero was already in the works for his own show, Loki (2021).
The first animated Marvel Cinematic Universe series.