"Omniscience is the quality of having unlimited knowledge." This definition leaves out "about what?" Say I know all about another person. My knowledge of the person is unlimited. Or I know all about algebra. That does not suggest I know all about everything else. That is the fallacy of the opening definition. Rather "omniscience" refers to having maximal knowledge about a topic or subject.
that if our heart condemns us, that God is greater than our heart, and He knows all things.
The actual Greek reads "He knows all." Leaving us to determine "all about what?" Here the idea is God knows all about our heart - our character, attributes and thoughts. So our individual understanding of our depravity is overruled by God's acceptance of our "clear conscious." It is wrong for us to think our opinion overrules God's assessment!
In summary, there is absolutely no support anywhere in scripture for the premise that God possesses "exhaustive foreknowledge." So rather than attempting to claim absurdly, that His exhaustive foreknowledge does not fix the future to the foreseen future, the objective bible student should realize scripture does not support Infinite Omnipotence.