Word – How to make columns the same (balanced) length (or depth) at the end of a document

Instead of using columns, just use a two column table. You can format the borders of the table to be invisible, and set the padding as you need it to maintain separation.

And this will roll over to new pages without issues, automatically.

You can't achieve it with column settings, instead:

To make the first column in the first page just insert a table of one cell (or a text box, that will do the same)

• set its height to be the same as the page's height
• set with to the desired value
• set text to be wrapped around it
• remove borders to make your first column look like the normal text.