Current ports version is 1.72.0_2 from Dec 2019. The boost team have made available 1.74.0 in August 2020. There are quite a few updates of the libraries, per: https://www.boost.org/users/history/version_1_74_0.html
Already in progress https://reviews.freebsd.org/D24485
*** This bug has been marked as a duplicate of bug 246106 ***