A fact is simply something which is true. Paris is the capital of France. That is a fact, Paris is defined as the capital. Beliefs don’t come into it, I can believe that Marseille is the capital of France but that doesn’t make it true. Someone believing that NASA are faking everything doesn’t make it a fact. Nor does believing that NASA are legitimate make that true of course but GPS works, Satellite TV works, Satellite phones work and so on. Rockets demonstrably lift off. Where do they go? Hundreds of people have now been to space, 7 of them were space tourists. There are weather satellites used by meteorologists, satellites taking regular pictures of the globe earth, lots of film from the ISS - an object which can be seen from earth.
To believe that there is a big cover up globally to pretend space travel is possible, fake all this footage from space, get all these people to lie about having been to space, make all this technology work in some other way other than satellites and fake a visible ISS somehow is a massive conspiracy theory. A lot of people would have to conspire to make all that happen. The only evidence I’ve seen for that conspiracy is a load of supposition and confirmation bias. But FE have to believe in this conspiracy because if space travel is real and satellites are orbiting the globe then clearly the earth cannot be flat.
As for a theory, the problem with that word is that in general use the word is used to mean a vague idea. In science though a theory is a model which explains observations and can predict the outcome of experiments. If those predictions fail then the theory should be amended or discarded.