Hello, Ole-Einar
Welcome to the Microsoft Community.
Hello, thanks for your feedback here on your issue, it sounds like you may have overwritten the data on the USB drive when you created the bootable drive.
Recovery tools sometimes have a hard time retrieving overwritten files, especially if the data has been replaced. However, if you can still open the .txt file on the USB flash drive, this is an indication that it is possible to recover some of the data.
You can try to use a more advanced recovery tool or a service specializing in file recovery, but success is not guaranteed. Successful recovery depends on how the data was overwritten and whether any part of the old file remains intact.
My suggestion is that you can only try some third-party advanced recovery tools or professional offline data recovery services that may help you get back more up-to-date files at this time, and a data recovery specialist should have the expertise to assist in the recovery accordingly.
Best regards
Bobhe | Microsoft Community Support Specialist