The env var will be provided at build time also.
We lack documentation on that but have an initiative to better cover this topic.
You can check out the following post, there is an example showcasing how to override ARGs: Dockerfile Deployment on High-Performance MicroVMs is GA - Koyeb.
Regarding your current configuration:
- remove the args override
- add an env var
FOO=apple
And everything should work as expected.
