The latest citus package on PGDG repos are for 8.0.0 version that was released on 2018.
Citus creates and maintains its packages in a seperate repository. You can use the instructions at Citus website to install that repository at https://citusdata.com/download
For a sense of completeness, here are the steps to install latest Citus 9.5 running on PG13 on Debian based distros: