I have not heard any DEFI lending for a mortgage because their business is based on digital collateral not physical.
There are projects in defi that work with real estate.
https://realt.co/https://realt.co/progress-of-real-estate-tokenization/The main problem is not defaults, but the lack of cryptocurrency legislation in many countries.
Even now, it is possible to tokenize all the world's stocks and trade them in a decentralized manner, but then all existing intermediaries will suffer billions of dollars in losses.