I opened my Mac with cmd+r command and erased old data. At least I think I did erase.
Then installed a new Big Sur from the same screen but there is still 70 gb unusable space in my disk.
macOS also asked me if I want to restore my old files when I first opened my Mac.
How can I find and erase those files ?
MacBook Pro 13″, macOS 11.7
I'm guessing you did not correctly erase your disk. While booted to the macOS installer, launch Disk Utility and click "View" and select "Show All Devices" so that the physical drive appears on the left pane of Disk Utility. Select the physical SSD and erase it as GUID and APFS (top option). The physical drive will be listed by its make, model, and size...something like "Apple SSD AP0128....".
I'm guessing you did not correctly erase your disk. While booted to the macOS installer, launch Disk Utility and click "View" and select "Show All Devices" so that the physical drive appears on the left pane of Disk Utility. Select the physical SSD and erase it as GUID and APFS (top option). The physical drive will be listed by its make, model, and size...something like "Apple SSD AP0128....".
Open Terminal (in the Applications > Utilities folder), execute the following command and post a screenshot:
diskutil list
This will show us all the containers and volumes on your disk.
I formatted my SSD but there is 70 GB used space from old files