Upgraded from Postman 7.x to 9.x. Virtually all metadata in my collections is GONE. Help!

I accepted the upgrade from Postman 7.x to 9.x and found that while collection entries are present, virtually all of the metadata (URLs, bodies, parameters, etc) are completely gone. We’re talking YEARS of data that will be very painful to re-create by hand.

I tried exporting and reimporting the data as someone suggested, but it made no difference. I also looked at old backups going back to 2019 and much of the metadata simply isn’t in any of the files. I tried downgrading Postman to older versions and reimporting, but that unsurprisingly made no difference. What on earth is going on?

I’m on Mac if that makes a difference. Please advise.