Is the interpretation of verses whose meanings are clear that comes to mind without reference to commentaries considered an interpretation based on personal opinion, and does disbelief result from it if it is correct, along with the need to repeat fasting and prayer?

There is no hadith indicating that whoever interprets the Qur’an by his own opinion is a disbeliever. Understanding the clear meanings of verses without referring to tafsir (exegesis) is not considered the blameworthy interpretation by opinion; rather, it is part of the reflection (tadabbur) commanded in the Qur’an. Reflection is obligatory for everyone according to their cognitive abilities. Whatever is clear in meaning can be understood, and a person is not burdened with what they cannot comprehend. Ibn Abbas divided the interpretation of the Qur’an into four categories, among which is that which people are not excused for being ignorant of, such as lawful and unlawful matters. An example of this is clear verses like the prohibition of carrion. One should be wary of interpreting the Qur’an by mere opinion, but far more dangerous is accusing oneself or judging oneself to be a disbeliever based on mere conjecture. Therefore, you must turn away from these whispers and strive against your own self.