The weight of a plane vs the lift generated by the wing will determine if it flies. Foamboard is better for larger size builds since it is more rigid and lower weight.
Card could be good for mocking up a design, since you can get large bits free from packaging but it will weigh more and be less rigid than foamboard. If you can’t get dollar store board, like we can’t in the UK, you can get similar 5mm board or 3-5mm Depron or foam online. Both those would probably be better than plain card for construction.
Try making the pizza box plane off the FT video, details are here.
I'm not sure if I understand your question. If you are making a small cardboard prototype of a plane, I'd say yes, try it in foam board. Using cardboard for a small model (10"-15" wing) is not going to be a fair test. The wing loading will be too heavy. If you made a normal size plane (35"-50" wing) I'd say no, probably not going to work in foam board.
I have found in my normal size planes a wing loading of 10-15 oz/sqft works well. But in a small indoor plane wing loading needs to be 1-2 oz/sqft. A 10X difference.
I have a buddy who always makes a paper prototype of his planes. He does this to find his ideal CG.