What is the linguistic difference between "yafʿalūn" (يفعلون) and "yaʿmalūn" (يعملون) in His, the Almighty's, sayings: "So do not grieve over what they used to do (yafʿalūn)" and "So do not grieve over what they used to do (yaʿmalūn)"?

The difference between "fi'l" (act/deed) and "amal" (work/action) lies in the fact that "fi'l" is general and can be attributed to both intelligent beings and non-intelligent beings, and may even be attributed to inanimate objects. Whereas "amal" is specific and rarely attributed to non-intelligent beings. Thus, "fi'l" is broader and includes what is done knowingly or unknowingly, intentionally or unintentionally, and can issue from humans, animals, or inanimate objects. As for "amal," it expresses the creation of an effect in something, and is often used for intelligent beings. Perhaps the secret behind differentiating between these two expressions in the Quranic verses is that "fi'l" was attributed to the people of Noah, likening them to beasts, while "amal" was attributed to the brothers of Joseph, as they were believing, intelligent beings.