You literally can’t see the trees through the woods when it comes to the ideal soil layer. Usually I go looking for knowledge online myself, but Youtube is full of it and also read a lot of untruths.
Linda Scott-Chalker is an American professional known for fighting myths and fake news in the field of agriculture. Usually she transforms dead ground into a new piece of blooming nature. They call it restoration. She did an experiment to show what the best soil layer is.
Her website is great because she tries to debunk some myths. So definitely worth taking a look there.
But this video is a masterclass of how the fork is really down. Thanks to research. So really worth it
Now Professor Karine Van Dorselaar also fell off her chair when she heard that we often use cardboard to stop weed growth. She was literally in shock.
Karine van Dorseleaar is senior lecturer in Materials Science and Ecodesign at Opleiding Productontwikkeling UA
Dear Trees,Karine Van Dorselaer
Here are some links that indicate than cardboard is not such a good idea. The composition of chemical substances is always different chemical cocktail. It is illegal to use recycled cardboard as food packaging, that also says it all…. https://www.gardenmyths.com/safe-compost-paper-cardboard/ https://www.paperonweb.com/chemical.htm https://www.foodpackagingforum.org/fpf-2016/wp-content/uploads/2021/06/FPF_Factsheet_Paper_Board_v1.pdf
The Food packaging Forum is an independent organization and a very reliable source.
Consider other possibilities. Layer leaves and above them a thin layer of wood chips to prevent blowing away. But forget that cardboard.