DietPi "E: Unable to locate package rockchip-fstab"

(reposting from “Using” forum) I’m getting this error:
root@DietPi:~# sudo apt-get install rockchip-overlay rockchip-fstab
Reading package lists… Done
Building dependency tree
Reading state information… Done
E: Unable to locate package rockchip-fstab

I’ve tried buster-stable and buster-testing repositories (each separately and also both together), but apt-get cannot find either rockchip-fstab or rockpi4b-rk-u-boot-latest.

This is using the DietPi distribution “DietPi_ROCKPi4-ARMv8-Buster.7z” pointed to from the Radxa site here: https://wiki.radxa.com/Rockpi4/downloads, following the steps on https://wiki.radxa.com/Rockpi4/radxa-apt to install the RockPi-specific packages

My hardware is a RockPi 4b v1.4 with 4GB RAM, with both a 32MB uSD and a 64MB eMMC.

When you use DietPi, you don’t need the packages, rockchip-overlay and rockchip-fstab.