[2023] Is it possible to retroactively use a sponsored sign on bonus be used after you installed the game but haven't played yet?

Originally posted by Airplayn: I probably goofed but after I installed the game but hadn't yet played I noticed one of the YouTube channels I watch sponsored bonuses but I'm afraid that these may have been limited offers for a new player.

You could try. Typically those bonuses are for new players and also some for old players. If it's a new bonus that can only be obtained through making a new account, then you won't be able to get it.