Can Fe and Ca react and become unusable in some foods?
Studies have indicated that calcium inhibits iron absorption in humans. However, numerous dietary factors influence iron absorption, and the effect of calcium may not be as pronounced when calcium is served as part of a whole diet. Calcium does not have any significant long-term effect on iron absorption. In addition, milk and milk products have not been found to affect iron absorption.
References:

Lönnerdal B. Calcium and iron absorption--mechanisms and public health relevance. Int J Vitam Nutr Res. 2010 Oct; 80(4-5):293-9. doi: 10.1024/0300-9831/a000036.
Grinder-Pedersen et.al., Calcium from milk or calcium-fortified foods does not inhibit nonheme-iron absorption from a whole diet consumed over a 4-d period, The American Journal of Clinical Nutrition, Volume 80, Issue 2, August 2004, Pages 404–409, doi: 10.1093/ajcn/80.2.404
https://www.dairynutrition.ca/nutrients-in-milk-products/calcium/calcium-and-iron-absorption-is-there-an-interaction