Is it permissible to pray Tarawih individually due to pain and inability to complete the prayer with the Imam, and then complete the remaining rak'ahs alone and perform Witr?

There is no harm in interrupting the Tarawih prayer due to the Imam's prolonged prayer combined with hardship. It is permissible to break the intention of following the Imam and complete the prayer individually. It is preferable to pray Witr at home so that the worshipper is not preoccupied with the Imam's recitation and prayer, and praying Witr individually is valid.