Why are my Numbers files from 2022 now "invalid"? Even more urgent: how can I get them back????

"NUMBERS FILE NAME XX can’t be opened right now. The file format is invalid."

What?????

I recently updated my Macbook Pro to OS Sonoma 14.5, which seemed like a good idea at the time. Is that why the Numbers spreadsheets that I created in 2022, all super-important to my business, are now inaccessible?

In this online support community, I've read older pleas for help with this same problem, some dating back to 2016, the most recent from 2023. Nobody ever seems to get help.

Is there really no solution to this problem? Have all my start-up business records vanished into a black hole, never to be seen again?

Apple Support, are you there???