Split a column in Numbers by extracting text in parenthesis
In order to accomplish this task, we need to use a combination of Text functions in our formulas. See Apple's documentaiton for more details on using these functions.

TL;DR the formulas are beneath the explanation.

So we need to identify the (XX) in each text string.  In one column, display only the parens and numbers between them, and in the other column, omit them.  This will require combining several text functions into a single fomula.

'Split A' Column

In the original 'string' each character has a position starting at 1.  So for example in the following string, the ( has a position of 3.

1 (23) Large Broom

So what we need to determine is at what position is ( and ) in each string.  We can use Find() to do this.
FIND(search-string, source-string, start-pos)

So using the example string above:
=FIND("(", "1 (23) Large Broom")
returns: 3

Then we can use FIND() to get the positon of ) too.  In this case it returns the position of 6.
We can now use this with the MID() function to retreive the number with parens.

MID(A2,FIND("(",A2),FIND(")",A2,)
// Where A2 contains our original text
result: (23)

Now, if there are no () we will get an error so to handle this we wrap the whole formula in the IFERROR() function.  If there is an error return an empty string.  (or anything you wish)

IFERROR(MID(A2,FIND("(",A2),FIND(")",A2,),"")

Paste this formula in your 'Split A' column.

'Split B' Column

We can use the REPLACE() function to substitue an empty string for our number in parens.  So this: (23) becomes this: "". (The quotes won't show.)
REPLACE(source-string, start-pos, replace-length, new-string)

To remove the (23), we need to add 1 to the position of ) then subtract the position of (.  So in this case 7 - 3 to get 4, the length of our number/parens string.
REPLACE(A2,FIND("(",A2,),(FIND(")",A2,)+1−FIND("(",A2,)),"")Breakdown:


REPLACE(
  A2, ← the source string cell reference
  FIND("(",A2,),
    (FIND(")",A2,)+1−FIND("(",A2,)), ← resulting in 4
"") ← replace with empty string


Wrap this also in a IFERROR() and now the result is 1  Large Broom  (Note the extra space.  This can be eliminated if we add 2 instead of 1)

TL;DR - So here we are. Whew! the formulas with our nested functions to solve this:

Split A

IFERROR(MID(A2,FIND("(",A2),FIND(")",A2,),"")

Split B

IFERROR(REPLACE(A2,FIND("(",A2,),(FIND(")",A2,)+1−FIND("(",A2,)),""),"")