hello is it possible to downgrade the firmware of mavic mini ?

I really, highly doubt it now.

You might be able to with DJI assistant 2 but I don't know why you would want to. The new updates have made several improvements

Yes you can in DJI assistant 2.

simple curiosity

I know they "killed" that "option" for the Mavic Gen I a while ago...

Hi, thank you for reaching out. We do have an option on DJI Assistant 2 for the upgrade and downgrade process for the DJI Mavic Mini. However, we do not recommend to perform the downgrade process with no further advice to avoid any possible errors. Please don't hesitate to reach us if you have any questions. Thank you for your continued support!

The new Yaw movement of the Mini is horrible, it seems don't present in the basic firmware, V01.00.001, and implement later, but it's uncontrolable....
So, me too, i'm looking for donwgrade it, until they implement the option to slow donw or fasting up the spooed of the yaw...