An alternative approach for your example data, and any data with an easily definable marker for the required text, would be to split the data into an array of lines (demarked at \n), apply an array filter to the array to remove elements not containing the marker string, and finally .map the array to contain just the required part following the marker string.

The processes can be strung together in a single line as demonstrated in the following snippet:

string = "hukhkhk\nClosing Date: Friday 22nd April 2022\nwdwqdwqdwqd\nClosing Date: Friday 22nd April 2023\newdewfewf";

markerString = "Closing Date: ";

datesArray = string.split('\n').filter(text => text.indexOf(markerString) > -1).map(text => text.slice(text.indexOf(markerString)+ markerString.length));

console.log(datesArray)

(?<=Closing Date: )(.*?)(?=\\n)

Starts matching after Closing Date: (space included)

Stops matching before the first \n it encounters

This worked on your example

live example

Edit:

1. I had to remove group names (were unused and making a breaking difference on runtime)
2. filtering empty strings (@input edges) as a result of split()

const input = "hukhkhk\\nClosing Date: Friday 22nd April 2022\\nwdwqdwqdwqd\\nClosing Date: Friday 22nd April 2023\\newdewfewf";
const regex = /(?:(?:\\n|^).*?(?:\\n|$))(?:Closing\sDate:\s)?/mg
const dates = input.split(regex).filter(date => date.length > 0);
console.log(dates);

Out:

[ 'Friday 22nd April 2022', 'Friday 22nd April 2023' ]

1st answer:

Using regex to find all non-date content:

const re = /(?<junk>(?:\\n|^).*?(?:\\n|$))(?<delimiter>Closing Date: )?/gm

Then using JS split to get array with dates only

const dates = input.split(re);