RazaTD's strawman was rooted in assuming that the Earth is not a celestial body. This is his original proposition, distinct from anything you'll find in the Wiki. Context is crucial.

So what doesn't have gravitational acceleration then? Since FE can't say much about the nature of the Sun and the Moon and being able to directly test them is not accessible to laymen and FEers don't trust NASA and their robots, they could assert that such celestial bodies are special for whatever reason. But Earth is right here and easily testable. If Earth exerts gravity, what property does it have that other matter doesn't which makes this possible? Are there special rocks deep down that work like magnets but for gravity?

Obviously, you don't want to end up with all matter exerting gravity otherwise it's not celestial anymore, and why even have UA then? This will basically be RE gravity which FEer make fun of.

However, the challenge is to prove that the force of gravity is much weaker than the RE value.

Once again, I'd appreciate it if you didn't waste our time with such bad faith arguments. It won't work. We will not presume the correctness in RET while debating FET, for reasons that hopefully don't need to be spelled out.

This is not a bad faith argument. I am not asking you to presume the correctness of RE model. I proposed a model that is similar (possibly not because you haven't clarified whether matter also exerts gravity) to the one you just suggested where even Earth exerts gravity. Now by logical necessity, this gravitational force must be less than that on RE model because UA also contributes to the overall gravitational acceleration on the FE.

Acceleration on RE = 9.81 (approx.)

Acceleration on FE = A (exact due to UA) + B (celestial gravitation)

A must be significantly larger than B because as A approaches 0, celestial gravitation basically becomes a different name for RE gravity.

A must also be strictly vertical while B is like a point source.

So, the task for FEer, only if they concede that matter exerts gravity (which you are just a few steps away from as you have just conceded that Earth has gravity), is to demonstrate that B is significantly less than 9.81, which is what RE claims is the gravitational acceleration.

I don't see where I have presumed the correctness of RE here. The value of gravitational acceleration 9.81 is what we observe. Making the assumption that it must be the same on Flat Earth does not mean I have assumed RE is correct. 9.81 is an observation that both models must derive.