Pasting fields with newlines in Numbers

Instead of clicking once to select the cell, double click the cell to enter text entry mode. Then paste.

It will paste it into a single cell. I misunderstood what you wanted to do.

If they have quotes around them like shown in your post and you are editing it in a text editor, save it as plain text with a CSV extension (in other words, make it a CSV file). Open that file with Numbers and it will be in individual cells in one column. Copy/paste to your original document.

It is unfortunate that Numbers does not recognize it as CSV data when copy/pasted directly from the text editor

You can replace newlines with two newlines using Find (Command F). If you do Replace All it will replace every one it finds in the entire document. There is a Shortcut app shortcut that will Replace All in selected cells only, rather than everywhere. If you need it I'll provide a link to it.