Will whoever lacks devotion in their prayer enter Hellfire and be considered a disbeliever because God did not accept their prayer?

Devotion (khushu') in prayer and contemplating its meanings is the spirit of prayer, without which it becomes mere movements. Allah has decreed the success of the devoted. It was narrated from Ammar ibn Yasir that prayer should be shortened to pre-empt whispers (waswas), and the Prophet, peace and blessings be upon him, said: "Indeed, a man may perform a prayer, and perhaps he will get nothing from it but a tenth of it..." Khushu' is meant to be: the devotion of the heart and its fear of Allah, or being attentive to prayer, or being still in it, or not talking to oneself. The prayer of one who lacks khushu' is valid according to the majority of scholars, and this is the agreed-upon correct view, and that khushu' is not a condition for the validity of prayer.