This project uses github actions for creating the zip file, please see the commands executed here: https://github.com/sullerandras/terraria-hd-textures/blob/master/.github/workflows/build.yaml
If you use Windows then you should be able to copy the commands from the github actions file and execute them on your local machine.
Alternatively you can fork this repo and enable github actions on your fork. After that you can create a pull request like this (against your own fork!) to build a release: sullerandras#12