Yes it's non-zero, though
https://www.capabilitieslimited.co.uk/pdfs/20210917-capltd-c... is a recent exploration of what it takes to port X11 and KDE to CHERI. Of the around 6 million lines of C and C++ code involved, only about 0.026% needed to be touched, or just under 1.6k. That number will of course vary significantly between the type of code; boring applications code generally doesn't need changes (e.g. htop and sudo built and ran out of the box for me recently, as examples), but language runtimes will need significant changes. Pages 21, 22, 26 and 27 of that report have the per-component breakdown of that number.