What would switch a Volto site's root to a "folder contents" view?

The site https://new.waverobotics.com/ is Plone 6.0.11 and Volto 18.0.0-alpha.38 (it's a clone of the 2024.ploneconf.org site code):

  • Volto 18.0.0-alpha.38
  • Plone 6.0.11
  • plone.restapi 9.6.1
  • CMF 3.5
  • Zope 5.9
  • Python 3.12.3 (main, Feb 4 2025, 14:48:35) [GCC 13.3.0]
  • PIL 9.5.0 (Pillow)

The site has been restored to an earlier backup but for a while the front page looked like the old folder contents view of Classic. I couldn't figure out how that had been changed, hence the restore. (Wasn't able to undo... got the usual message "MultipleUndoErrors: Undo error 0x219a: Undo error 0x219a: Some data were modified by a later transaction")

This is what it looked like before the restore:

and this is what it should look like:

Interestingly, on the restored site it's the folder listing view that's selected: