Although Pages '09 used carriage returns for paragraph and hard returns, Pages v5 through the current v14.2 only support line feeds. If you open a Word document, Pages will translate carriage return/line-feed pairs to line feeds. Pages '09 documents will have their returns translated into line feeds.
Pages '09 never gave one the ability to find/replace strictly selected text, and neither does the current Pages. The whole document gets involved. In MS Word, one has many more control characters to choose from, both in find and replace, and one can work on a selection of text.
If you want to effect a text selection in Pages, you will first need to copy/paste that into a Rich text TextEdit document, or another external text editor, make the change there, and then copy/paste that result back into Pages.
Tested: Pages '09 v4.3 macOS Mojave 14.6, and Pages v14.2 Sequoia v15.0.1.