Omg got ittttt thanks to @yvmuell it was indeed a driver I did not use properly.
Thank you ALL SO MUCH for your help !
In case it can be useful for others, here is what helped me
- download the Google USB Driver zip file.
- Extract the downloaded file.
- Now, press the Windows + X key simultaneously, and from the context menu, choose Device Manager.
- Expand the portable devices option.
- Right-click on the smartphone name you have connected with the computer using a USB cable, and choose the Update driver option.
- In the following window, choose the Browse my computer for drivers option.
- Click on Let me pick from a list of available drivers on my computer .
- Click on Have Disk option.
- In the prompt that pops up, choose the Browse option.
- Select, and open the android_winusb.inf file available in the Google USB folder.
- Now, click on OK.
- Select the Android bootloader interface from the following window and click on the next option.
- Choose the Install option from the prompt that pops up.
- That’s it. You have finally installed Android bootloader interface drivers on your system.
- Now you can see the Android Bootloader Interface option under the Android Device option.
- Now open Command Prompt in administrator mode on your Windows PC.
- Type the below-mentioned command and press Enter.
fastboot devices
That’s it. This time, Fastboot will work on your system and detect your Android smartphone.