As of v3.0.6 this apparently requires zstdmt, not just zstd, which is a major departure. I have not found any Windows binaries for zstdmt. I'm not sure it's available elsewhere either.

This is what happens:

##[debug]Archive Path: C:\drud-actions-runner\_work\_temp\ff5371eb-5f15-4474-8084-5df62fc397fa\cache.tzst "C:\Program Files\Git\usr\bin\tar.exe" --posix --use-compress-program zstdmt -cf cache.tzst --exclude cache.tzst -P -C C:/drud-actions-runner/_work/ddev/ddev --files-from manifest.txt --force-local /bin/sh: zstdmt: command not found /usr/bin/tar: cache.tzst: Cannot write: Broken pipe

It was already hard enough to get zstd onto Windows... It's sad to break things now by changing the tar compression format even father.

Previous instructions for getting zstd into a Windows machine were at #580 (comment)