The current baseline check AX_BOOST_BASE(1.47)in configure is unchanged since 2013 (<https://gerrit.libreoffice.org/plugins/gitiles/core/+diff/0d5b9f1ad4b132d8d0cc22af1f524f971c0166db%5E!> "check for boost >= 1.47 and SHA512_CTX (openssl >= 0.9.8) in configure"), and is likely no longer meaningful (in the sense that presumably nobody would try a build of recent LO with such an old Boost anyway).
The latest version offered at <https://www.boost.org/> is 1.72.0, and our bundled external/boost is 1.69.0 on libreoffice-6-3 and -6-4 and 1.71.0 on master.
<https://gerrit.libreoffice.org/c/core/+/90770> "Fix build with boost < 1.68" is a request to make libreoffice-6-4 build with older Boost, so there is apparently demand for that (though the Gerrit change lacks further information what that demand looks like exactly, i.e., what version of Boost, and why people would be stuck with that version).
There is also back-/forth-ports of that Gerrit change to libreoffice-6-3 (<https://gerrit.libreoffice.org/c/core/+/90808>) and master (<https://gerrit.libreoffice.org/c/core/+/90807>), but it is unclear to me whether those are borne out of any actual demand, or were merely done "over-enthusiastically" in response to my question "Why would this only be necessary on libreoffice-6-4, but not on master?" (<https://gerrit.libreoffice.org/c/core/+/90770/4#message-1f2f934499721fea91e333ddc1f6e08bdfb766a1>)
I would like to start a discussion about the actual Boost baselines we need to support on libreoffice-6-3, -6-4, and master. Lacking any communicated reason why a branch should support a specific lower baseline, I would suggest we stick to the version of our bundled external/boost on a branch as the baseline for that branch (and update the configure.ac AX_BOOST_BASE check accordingly).