I updated it to support a21.
You can convert a19/a20 prefabs for a21.
I have not checked it too much, but that is based on the previous version, so I don't think it is a problem.
Download "7DTDPrefab19to21_0.1.0.0.zip" from here.
I made a tool to convert the prefab made with a19 so that it can be read with a20, so I will publish it.
Download "7DTDPrefab19to20_x.x.x.x.zip" from here.
Please read the included Readme_En.txt carefully.