As far as we know, Isaac Newton did NOT endorse the flat-earth theory, so no need for the mainstream science community to freak out! 😋
However, Newton wasn't completely a proponent of the heliocentric model. He did leave open the idea that the earth was motionless, at the center of the universe. In other words, Newton didn't entirely dismiss the geocentric model of the universe.
Newton wrote:
In order for the Earth to be at rest in the center of the system of
the Sun, Planets, and Comets, there is required both universal
gravity and another force in addition that acts on all bodies
equally according to the quantity of matter in each of them and is
equal and opposite to the accelerative gravity with which the
Earth tends to the Sun...Since this force is equal and opposite to its gravity toward the
Sun, the Earth can truly remain in equilibrium between these two
forces and be at rest. And thus celestial bodies can move around
the Earth at rest, as in the Tychonic system.
What's truly interesting is that our education system (and I'm assuming all education systems throughout the world) teach that the heliocentric model has been proven beyond a shadow of a doubt.
But that's simply not true!
Nothing states that the geocentric model is impossible; indeed, another force could exist that would allow this model to be possible, as Newton asserts.