Thanks for sharing more details! Would you be willing to share which pre-postgres 14 install you were upgrading from? That could give some clues.
You're talking about published form previews, not draft previews, right?
When you go to your form > Submissions and then click the + New button, does that work? The new submission link and preview link should be identical except for an added /preview part of the URL after -. Maybe comparing the + New and preview URLs could also give clues.
Is the behavior the same for all forms? Do you have any forms that only have one published version that you could try?