Al-qaza' is what the Prophet ﷺ forbade. The Prophet ﷺ said: Take it all off or leave it all.

All of it. And when Nafi' was asked about al-qaza', he said: It is to shave some of the hair and leave some.

The issue of whether it's with a razor or not, it's if it's visible.

Even if it's not with a razor, but the hair is thick, for example, and from here.

Not with a razor, with a machine, but it's clear, meaning it's obviously different from this part.

This is al-qaza'. But if it's something slight, what they call layered.

Yes, this is a gradual cut, and there is nothing wrong with it, insha'Allah the Exalted. But if it is clear to the point that this part is different from that part, and anyone who sees it can clearly notice it from near and far.

Then this is the qaza' that is not allowed, and Allah knows best.