Is the saying: "Inflation will increase if women do not wear Hijab" correct and mentioned in the Sunnah, or does it have no basis?

There is no specific Hadith with this meaning. However, the sacred texts indicate that inflation and all other types of afflictions occur due to the sins of people and their transgression of God's limits. The root of every religious or worldly calamity is the servant's sin, as stated in the Almighty's words: "And whatever strikes you of disaster - it is because of what your hands have earned," and "Say, 'It is from yourselves'," and "Whoever does evil will be recompensed for it." It is also mentioned in the Hadith: "Indeed, a man may be deprived of provision because of a sin he commits."