If a mental image of what Allah SWT looks like pops up in your head, even though you know Allah SWT is greater than what any of us can ever imagine, does that make you fall outside of Islam?
Jazak Allah Khair
Thinking about Allah S.W.T can be understood in two meanings and ways. Firstly, one thinks about Allah by equalizing Him to the substance and nature of Allah S.W.T. While the second meaning is thinking about Allah S.W.T in the sense that he remembers Him (zikrullah).
If we think about Allah by referring Him to substance of God then this is prohibited. Plus, if one pray to the substance of Allah instead to Allah Himself, then this is considered as denial (kufur).
However, if one thinks about God by doing zikrullah and reciting the Quran then this is demanded and encouraged.
Wallahwualam. Let us pray to Allah S.W.T to give us a good understanding on Islam. Ameen.
Nothing will make you fall out Islam, except worshiping but ALLAH.
Imagining Allah SWT, and what does he may look like or how does he act or even if he actually is there, is called Waswas from Shaitan. You need to To seek refuge from it, and keep your mind busy with other useful things like Zikr and Qur'an.