If you know about the bug, but manufacturer does not provide any patches, you can still mitigate it, put in place detection measures or just stop using that sof

If you know about the bug, but manufacturer does not provide any patches, you can still mitigate it, put in place detection measures or just stop using that software. You can't (necessarily) do those if you don't even know about the bug yet as it hasn't been published. That's why 0day is a useful term.