Hello Riccardo Scagnoli,
You have two options to manage the featured image.
1. Globally From Customizer
2. From individual post setting (Edit the post and scroll down to find the options)
If you set the featured image hide globally but the featured image is enable on post setting:- 2, it will take the 2 setting.
Means the priority of taking setting is greater of 2, not one.
Hope you understand what we mean.
Regards