The package should support it; I'm working towards making neovim available on those arches.
commit 82e44d26c051c0d8409a843879afe09674f4a68b Author: Mikle Kolyada <zlogene@gentoo.org> Date: Sat Apr 20 22:00:41 2019 +0300 dev-libs/libvterm: Add ~arm keyword wrt bug #676688 Signed-off-by: Mikle Kolyada <zlogene@gentoo.org> Package-Manager: Portage-2.3.62, Repoman-2.3.11 RepoMan-Options: --include-arches="~arm"
arm64 keyworded, closing