是的，当 what 为融合型关系代词时，它不可外置，即不可以与形式主语或形式宾语连用，此时总是直接用作主语或宾语。如：

1. 直接用作主语

What he says is pure rubbish. 他所说的纯粹是废话。

What I like about the job is that it’s never boring. 这份工作我喜欢的是它从不枯燥。

What he needs now is a lot of tender loving care. 他现在需要的是充分的关心和爱护。

不能说：

It is is pure rubbish what he says.

It is that it’s never boring what I like about the job.

It is a lot of tender loving care what he needs now. 

2. 直接用作宾语

I found what he said very interesting. 我发现他说的很有趣。

We consider what he said very useful. 我们认为他说的很有用。

不能说：

I found it very interesting what he said. 

We consider it very useful what he said. 

但是，如果what是表示疑问语气时可以用形式主语或形式宾语。如：

Does it matter what I want? 我要什么重要吗？

It’s none of your business what I’m doing. 我在做什么与你无关。

He made it clear what he liked. 他清楚表明他喜欢什么。