Open parole either with entries in playlist or have a playlist active. Play button is inactive until something is played by double clicking on a playlist entry.
Sean Davis referenced this bugreport in commit 81e9ec60313104346b5753ea19e1aa1ab3e468ad Enable play button when single item is added to playlist (bug #13724) (LP: #1705243) https://git.xfce.org/apps/parole/commit?id=81e9ec60313104346b5753ea19e1aa1ab3e468ad
Fixed with the above commit.