This summary is by Sam Liddicott in the mailing list:

Libre office has two ways of inserting columns.

If a page or frame has columns, then one column is filled, before the next receives any content. In these cases columns have a fixed height, which is equal to the height of the page or frame.

If a paragraph has columns, then the height of the paragraph is such that all the columns are filled evenly with content.

The second way is the way texmacs does columns, using <with|par-columns|2|...>

So the question would be, does texmacs also have page columns? I think it does not. I tried inserting an elastic vertical space but it did not extend the block to the bottom of the page.