Hi everyone,
if you want to check your Windows Product Key without installing anything, just open Command Prompt as administrator and run this command:

reg query "HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\SoftwareProtectionPlatform" /v BackupProductKeyDefault

You’ll see something like this:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\SoftwareProtectionPlatform
    BackupProductKeyDefault    REG_SZ    XXXXX-XXXXX-XXXXX-XXXXX-XXXXX

If nothing shows up, it means your Windows is activated with a digital license (linked to your Microsoft account or hardware), so there’s no visible Product Key stored in the registry.