I have found a way to change the connecting arrow text size but it feels hacky. This works for me 100% of the time. I am using the Figma desktop app on Mac (116.2.4)
Steps:
- Click to make a regular text element and set the font size to the desired size (I chose medium, the default labels are tiny).
- Add a new label to the connecting arrows and start typing. The text size should be the same size as the text element you created.
- Delete the unneeded text element. You are only creating the text element to piggyback on the font change.