What is the ruling on fidgeting with clothes, cleaning one's nails, or looking at a watch during prayer, especially when the Imam is reciting?

Sheikh Ibn 'Uthaymeen mentioned that movement during prayer is makrooh (disliked) unless there is a need for it, and it is divided into five categories: Waajib (obligatory), such as purifying oneself from impurity or facing the Qiblah; Muharram (forbidden), which is excessive continuous movement without necessity, as it invalidates the prayer; Mustahabb (recommended), such as moving to straighten the saff (row); Mubaah (permissible), such as slight movement due to a need, or extensive movement due to necessity, like praying during combat; and Makrooh (disliked), which includes any other type of movement, such as fidgeting with a watch or nose. The movement that invalidates prayer is that which contradicts the nature of prayer, making the worshiper appear as if they are not praying; this is extensive continuous movement, and there is no specific number to define it.

Sheikh Ibn Baaz added that a believer should approach their prayer with full attention and khushoo' (humble submission) in both heart and body, and that ṭuma’nīnah (tranquility) is a fundamental pillar without which the prayer is not valid. Excessive fidgeting invalidates the prayer, and slight fidgeting is makrooh. However, slight movement according to custom, or extensive non-continuous movement, does not invalidate the prayer. Among the proofs for the permissibility of slight movement are the Prophet's (peace be upon him) opening the door for 'Aishah while he was praying, and his carrying Umamah, his granddaughter through Zaynab, during prayer.