Can I use this platform to prepare state returns only?

[AnnetteB6]

No, state returns get the majority of their information from the Federal return.  Therefore, a Federal return must be completed first.  

This is true regardless of whether you intend to electronically file or file by mail.

[Mike9241]

Even if you completed the federal return using TurboTax to get the state return, it would have to be mailed because the federal return apparently was not e-filed through TurboTax.