Sorry to say, but this question is extremely clear and descriptive, as-is.
Microsoft Word has had a function for at least 10 years, originally in the Print Preview pane, “shrink by one page.” It’s a function that examines the entire document and does what it can to reduce page occupancy so as to reduce the overall page length by one page. Designed for the use case of professional correspondence where a small paragraph or a few lines of material wrap onto the next page at the end, so that the final version would otherwise feature a last-page of the document with a lot of whitespace. It can cause confusion, it can cause miscommunication in the event of the last page being separated and misplaced by the recipient (especially when the final page is also page 2) and frankly, it’s a waste of paper when printed.
The “shrink by one page” function often reduces body text by half a point-size, and also does similar with margin / header / footer text. I am also curious how LO handles this.