Does the ruling on hidden melodic errors in prayer differ between intentional and unintentional, and does the lack of mastery of the obligatory lengthening (madd lazim) due to not learning the rules of Tajweed affect the prayer?

Observing the madd (prolongation) and its duration in vowel counts is a recommended aspect of tajwid, the omission of which does not invalidate the prayer. Do not make things difficult for yourself or repeat the word more than once, as the matter is simple. Scholars in this field define a vowel count by the duration of clenching or unclenching a finger, but it is better not to do so during prayer to ensure complete humility and presence of heart. Imam Ahmad himself hesitated regarding the permissibility of counting tasbih with the fingers.