cavity closure

Solutions for this cavity against the wall below door frame. Looks like previous had new flooring installed. The threshold going outside is fine.

Hi all, I hope you are well. I am looking for some advice on our extension and how to close our cavity floor to install a bi-fold door. Currently we have a 2.05m high by 2.0m wide area for the bi-folds. On the external wall is a layer of stone directly on the blocks which has a DPC and is...