Is true that $L_1 = \{01^*0\}$ is $m$-complete in the class of decidable languages?
Your approach can't succeed. You're asked whether every decidable language reduces to&nbsp;$L_1$ but your approach is to try to show that some undecidable language doesn't reduce to it. That would show nothing about decidable languages.

But are you sure that your definition is correct? Every language except $\emptyset$ and&nbsp;$\Sigma^*$ is $m$-complete by the definition you give.