Does the worshipper miss the rak'ah if the Imam rises from rukoo' before the worshipper, who joined the prayer with him from the beginning, bows for rukoo'?

It is not permissible to fall behind the Imam. However, if you fall behind him due to an excuse, such as slow recitation or forgetting the Fatihah, and then you catch up with the bowing and follow the Imam, your prayer is valid. But if you fall behind him without an excuse, scholars have differed regarding the validity of the prayer. Some have favored its invalidity, and in this case, you are required to repeat it.