Does the prayer become a supererogatory one if I miss a rak'ah, and I am in the tashahhud, and the imam begins to say the taslim, and I stand up to make up what I missed before the imam finishes the taslim?

If the ma'mum (follower) stands up to make up the missed rak'ah (unit of prayer) before the imam (leader) completes the first tasleem (salutation), their prayer becomes invalid and does not turn into a nafl (supererogatory) prayer. However, if they stand up after the imam completes the first tasleem but before completing the second tasleem, their prayer is valid according to the majority of scholars.