libflann-dev 1.9.1+dfsg-7 (amd64 binary) in ubuntu focal

 FLANN is a library for performing fast approximate nearest neighbor searches
 in high dimensional spaces. It contains a collection of algorithms found
 to work best for nearest neighbor search and a system for automatically
 choosing the best algorithm and optimum parameters depending on the dataset.
 .
 This package contains development files needed to build FLANN applications.