regarding indirect Interrogative questions and WH Conjunction

Question

1. It is clear that what was done as a public health measure to protect people from the COVID-19 threat has snowballed into a major economic crisis for the urban poor general.
2. I didn't not understand what the government's intention was behind this scenario.
3. I didn't understand that what is the government's intention behind this scenario.

Which one is correct?

In the first sentence 'that and what' are used together. Why? Can we?

The second sentence is an indirect question where WH words work as conjunctions.

Shall we consider the third one incorrect?

Answer 1

Sentence 1 can be simplified by removing its starting phrase "It is clear that...".

The following word what is an interrogative pronoun that introduces the clause

what was done as a public health measure to protect people from the COVID-19 threat...".

That phrase is the subject of "has snowballed..."

Now, the entire sentence starts with the phrase "It is clear that...", which makes everything after it a dependent clause introduced by the relative pronoun that.

Here is a simpler example of the same use of that and what next to each other:

I think that what we did was good.

In your sentence 2, what is also an interrogative pronoun, making what follows into a noun phrase, which is the direct object of "understand"

Your example 3 is not grammatical.

Answer 2

1. It is clear that [what was done as a public health measure to protect people from the COVID-19 threat] has snowballed into a major economic crisis for the urban poor general.

In this sentence, 'It' = that . . . . . . poor general.

Here, the that-clause is in apposition to the pronoun 'It'. So, the that-clause is a nominal appositive clause.

The bracketed part is the subject of the verb phrase "has snowballed".

So, this sentence is grammatical.

2. I didn't understand [what the government's intention was behind this scenario].

Here, the indirect question [the bracketed part] is the object of the verb "understand". So this is also a nominal clause as an object of a finite verb.

So, this sentence is grammatical.

3. I didn't understand that what is the government's intention behind this scenario.

What means 'that which'. In this sentence, 'that' should be omitted. The what-clause is a subordinate nominal clause. So it should be an indirect question. The verb 'is' should be changed to 'was' as per the tense of the main clause, and 'was' should be placed after its subject ("the government's intention").

So, this sentence is ungrammatical.