I was able to recover the broken file by means of following steps:
- Run audacity project tools on the corrupted file.
$ audacity-project-tools -recover_db -recover_project broken.aup3
- Get a error message similar to this:
Project requires Audacity xx.xx.xx
Unsupported project version.
Note that required version may change, e.g., 71.211.6.
- Open the file in an Hex-Editor, e.g., “Hex Editor Neo”
- Identify the version required in the first rows of the file by using an ASCII Code Table, e.g., 71 is displayed by 0x47.
- Change the corresponding fields to 0x00 or something lower or equal than your current Audacity version.
- Save your changes.
- Try to open the file in Audacity. If still an error appears, follow the next steps. Else you are fine
- Run audacity project tools on the modified file.
$ audacity-project-tools -drop_autosave broken.recovered.aup3
- Open the resulting file, i.e., broken.recovered.recovered.aup3 in Audacity and acknowledge the warning. The project is recovered.
You may want to append it to the recovery guide in this forum