As previously stated, Ridley was not originally present in Metroid II: Return of Samus. Therefore, his appearance in the remake Samus Returns is a retcon.
It was MercurySteam's idea to add Ridley into Samus Returns as the surprise final boss. Yoshio Sakamoto approved of the concept, believing that fans would love it and it would make the story more dramatic. While there is no direct link between the 2D and Prime series, Proteus Ridley's cybernetics from Meta Ridley were included to preserve a minimum level of consistency in the timeline.[1]
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The Proteus Ridley boss battle in [[[Metroid: Samus Returns]]
↑Yoshio Sakamoto: "In fact, it was MercurySteam's idea to use Ridley as the final boss. I knew it would be a surprise and that the fans would go crazy, so I gave my approval right away! I think it makes the story even more dramatic!" "The Metroids (2D) in which I have worked and the Metroid Prime are two different sagas; there is no direct link between their stories. When the Prime saga started, I agreed with its producers that we should try to preserve the timelines and a minimum level of consistency, but also to be free to create the games that we considered appropriate and avoid doing anything that would coerce the other."(translated from Spanish) https://www.hobbyconsolas.com/listas/asi-hizo-metroid-samus-returns-entrevista-yoshio-sakamoto-279253?page=1