TL;DR: as of open-next 2.2.0 Next 12's preview mode does not work, when accessing a route that sets the preview mode cookies (e.g /api/set-preview?slug=redirect-me-to-here), the initial preview mode cookies are set, but when navigating to the resulting page, it 404's and preview cookies are unset.
As discussed in Discord https://discord.com/channels/983865673656705025/1186653005945245746
TL;DR: as of open-next 2.2.0 Next 12's preview mode does not work, when accessing a route that sets the preview mode cookies (e.g
/api/set-preview?slug=redirect-me-to-here
), the initial preview mode cookies are set, but when navigating to the resulting page, it 404's and preview cookies are unset.open-next 2.1.5 works as expected.