I have developer tools on a loot of drons from dji but on mavic mini I can't activate and I don't understand why? Please help me to understand what happened? And how to fix it?

As far as I know Mavic mini does not support SDK development.

It’s about time DJI release the codes. Many people which that Litchi add the Mavic mini to its list.
It will also add extra features.

The Mavic Mini is not yet supported by the Mobile SDK but will be included in the release around July 2020. See this post: Mavic Mini SDK Support for updates