Is saying "if only" in regret over a worldly matter or as an objection to destiny considered minor shirk? And how can one distinguish the "if only" that is considered minor shirk?

The utterance of "if only" (لو) in this context indicates a weakness in Tawhid (definition) (monotheism) and belief in divine decree (Qadar (definition)), because Satan enters the heart, making one think ill of their Lord, His decree, and His preordainment. This ill-thinking weakens Tawhid and prevents the servant from achieving faith in divine decree and the actions of Allah. Many object to divine decree concerning their own actions, imagining that if they had done certain things, the situation would have changed, while Allah has already decreed both the action and its outcome. There is no evidence that uttering "if only" in this context constitutes minor Shirk (definition) (polytheism).