Answer
The unstable MnF$_4$ forms, which theb spontaneously decomposes into MnF$_3$ and F$_2$.
Work Step by Step
Christe's preparation of F$_2$ is not direct chemical oxidation, but rather it involves the formation of unstable MnF$_4$, which spontaneously decomposes into MnF$_3$ and F$_2$.