To earn the platinum trophy in Guess the Word, first go into the Settings menu and enable Kids' Mode. After doing that, you will have to play through 50 levels. In each level, repeatedly press the R1 button until that level's correct word is, and then enter that word. The word for each level is randomly generated, so you cannot look up a list of them online.
This game has cross-save, so after earning the platinum trophy in the PS4 version, you can load up the PS5 version and auto-pop all trophies there.