why flat earth theory is correct in a meaningful way

Why?

1. A scientific "theory" is a well-accepted model that represents the world in a consistently useful manner
2. A model does not need to be correct, just useful
3. We use flat-earth approximations all the time

Just like we use Newtonian "classical" physics despite knowing more accurate models, just like we use lower-precision constants, we can make use of approximations that we live on a flat earth.

Meaning, the following theories are also correct given they're generally useful in some scenarios:

1. Point-mass Earth
2. COBE sky cube Earth
3. Torus Earth
4. Massless Earth
5. Motionless Earth
6. Perfectly spherical Earth