There is a new pull request by AluisioASG against master on the void-packages repository

https://github.com/AluisioASG/void-packages xbps-zstd
https://github.com/void-linux/void-packages/pull/12657

etc/defaults.conf: mention zstd package compression support
Seems this didn't get updated in tandem with xbps 0.54.

A patch file from https://github.com/void-linux/void-packages/pull/12657.patch is attached