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

https://github.com/ndowens/void-packages amsynth
https://github.com/void-linux/void-packages/pull/26815

amsynth: update to 1.12.2
Remove patches, as they are implemented in this version

A patch file from https://github.com/void-linux/void-packages/pull/26815.patch is attached