レッドサーティーンは今回ゲスト扱いで操作キャラではないんだとさ

He’ll fight along you as an AI-controlled guest character.

“We felt the point at which Red XIII joins the party in the story is very late on so we thought okay, if we’re gonna have him as a full character and try and get the player to enjoy his character development arc and growth as a character through that,
it’s not really enough time to do that,” Final Fantasy 7 Remake co-director Naoki Hamaguchi told VG247 as part of a wider FF7 Remake interview.

“We thought that the best way to have him involved was as a guest character. Normally throughout the game you’ll be playing as a three-man party,
but you will have him as a guest character that fights alongside you during the the last part of the story,” Hamaguchi elaborated.
“He’ll be using all of his old really nostalgic moves, and you’ll see that. We felt that was the best way of showing him off as a character and who he is. That’s why we felt that was the best way to include him.”

https://www.vg247.com/2020/03/02/final-fantasy-7-remake-red-xiii-guest-character/