Hi. I decided to continue this project during the GameDev TV Game Jam 2022. Here is the result of around 110h of work for about nine days 
What I can say is that using Mixamo animations in Blender and exporting them into Unity is not that easy (I left that behind to focus on environment modeling and creating the gameplay).
And also colors and ligthing are quite different in the two programs 
Anyway, a lot to do better in the not so distant future 