Line height sets how far apart the lines of your notes are. Default is how notes have always looked; Compact fits more on the screen, and Relaxed and Spacious give long notes more air. It is in Settings under Appearance on desktop and mobile, on every plan.
On desktop
Open Settings, go to Appearance and open Line height, between Text size and Note font. Pick Compact, Default, Relaxed or Spacious, and every open note follows at once.
On mobile
Open Settings, tap Appearance, then Line height, under Text size. Each choice has three small lines beside it, drawn as far apart as it sets yours. Tap one and the page closes.
What changes
The text of your notes: paragraphs, lists, checklists, quotes and the text in tables. Headings and code blocks keep their own line heights, and the chat, menus and settings stay as they are.
Text size and Line height work together: one sets how big the words are, the other how much room each line gets, and between them they set how dense a note reads. Small text on Compact lines fits the most on a screen, large text on Spacious lines the least.
Line height works with pages and focus mode too. On A4 or Letter pages the page breaks follow the new spacing, so a note set Spacious takes more pages than the same note set Compact. Pair it with a note font to get the page you want to write on.
It follows you
Line height syncs with the rest of your settings, like the note font, so a note reads the same on your laptop and your phone. Text size is the one that stays on each device. The chat can change it for you as well, like make my line spacing more relaxed, see Change settings from the chat.