The current version of the plugin is stuck at 3.19.6, which prevents installing the new version of hplip, and there is already a pull request for the latest version of the plugin. The request is four days old now.
commit 15a06b1f3faadef07b9e4b6b36c05add50a5534b Author: Manuel Rüger <mrueg@gentoo.org> Date: Sun Nov 24 21:33:26 2019 net-print/hplip-plugin: Version bump to 3.19.11 Package-Manager: Portage-2.3.76, Repoman-2.3.16 Signed-off-by: Manuel Rüger <mrueg@gentoo.org>