It seems like every other package in artifacts can be downloaded from the UI as a zip except universal artifacts. Why is that?
Currently, you must use the Azure CLI to download the Universal Package. Azure DevOps doesn't support direct HTTP/HTTPS download links or other ways to download the package.
az artifacts universal download --organization https://dev.azure.com/fabrikam --feed FabrikamFiber --name my-first-package --version 1.0.0 --path .
I've noticed there is already a similar feature suggestion in the following link, you can vote it:
https://developercommunity.visualstudio.com/idea/495533/download-universal-package-trough-api.html
More details please refer to the following documentation: