In Nebo, you can’t customise the page templates. Both Nebo and freeform pages are fixed, you don’t get any options to change them. Nebo pages are ruled/lined, whereas the freeform ones are squared or grid-patterned. Learn more about the different pages you can create in Nebo.
Even though you can’t change the page templates, you can adjust the line spacing of pages in Nebo. On the homepage, go to Settings (bottom of left sidebar) > Writing > Text display. You can then adjust the font size and line-height. Both affect your line spacing on the page. You can try out the changes before returning to your notebook.
Freeform pages have no line-spacing adjustments. However, unlike with Nebo pages, you can zoom in and out of your pages. The app displays the percentage zoom on the screen. It ranges from 41-200%.