in what is hoped

[Maybo]

What’s the difference between “in what” and “in which”?

 

[5jj]

'In which' is incorrect.

 

[Maybo]

'In which' is incorrect.

How about “that which”? What does “what” refer to?

 

[5jj]

'That which' is not possible, though it expresses the dual idea of 'which'.

 

[Barque]

How about “that which”? What does “what” refer to?

Instead of suggesting alternatives, please read this to understand what the sentence means.

The artwork ... is planned to be kept in Irpin, in what is hoped to become a square for modern art.
You can read this as: The artwork ... is planned to be kept in Irpin, in a place that is hoped to become a square for modern art.

The word "what" here means "a place that".

Similarly:
He scored what is considered one of the greatest goals ever.
This means: He scored a goal that is considered one of the greatest goals ever.