Neither any Manjaro branch nor even Arch provide such a version.
You have to get it from, for example, the aur package libtorrent-rasterbar-git.
Ex:
$ yay libtorrent-rasterbar
...
5 aur/libtorrent-rasterbar-git 2.0.0.RC.r584.ge0d9d7791-1 (+5 0.14)
A C++ BitTorrent library that aims to be a good alternative to all the other implementations around (git version)
...
(though the Arch package has been flagged out-of-date so there might be an update sometime … oops scratch that, Arch-Testing is on 1.2.10-6, so 1.2.11 probably isnt coming very soon)