amautertt
You develop your algorithm and you prove a bunch of theorems about it at the same time, incredibly difficult but totally wild!
There's some scattered projects like this https://github.com/OUPL/MLCert
I really believe, the volume 3 of SF series is a more polished and more approachable book.
https://softwarefoundations.cis.upenn.edu/vfa-current/index....
I am halfway through the first book (doing ALL exercises), I hope by next year end I would really like to finish vol 3.
This Isabelle books seems to cover more ground though.
I think these two are excellent books, SF : Logical Foundations for the basics, SF: Verified Functional Algorithms.
Unfortunately there is no royal road in type theory. This subject is incredibly demanding yet satisfying.
Software foundations are excellent books to read even if you aren't interested in verification/program proof.