I'm glad you were able to get access to your files again, but modifying the file system should never be done in order to recover data especially if you don't have a backup. Doing so can make it difficult to impossible for even an expensive professional data recovery service from being able to recover data from a drive.
For future reference and for any others with this issue I would advise trying these steps:
First check the health of the drive by using DriveDx and installing the special USB driver when prompted. Any "Warnings" or "Failing" notices mean the hard drive is worn out or actually failing respectively. If a hard drive has any "Failing" notices, then stop using the hard drive immediately since the more the hard drive is powered on and used the worse the failure is likely to become where even an expensive professional data recovery service may be unable to recover any data. Unfortunately these types of apps don't always correctly interpret the health of an SSD (usually they report a failure when the drive isn't actually failing).
Next once the drive is verified to be healthy try mounting the drive in read-only mode. You will need to use the Terminal command line to do this. Mounting in read-only mode may allow you to mount the drive even if file system errors are detected.
If the drive is healthy and using the HFS+ also known as MacOS Extended (Journaled), then you can try using the paid third party app Disk Warrior to attempt to repair the volume if First Aid was unable to do so. Disk Warrior is the best HFS+ file system repair utility available. Unfortunately Disk Warrior is not able to repair an APFS volume since Apple has not released the necessary APFS documentation so third party utilities can repair an APFS volume.
If the drive is healthy you can try using a data recovery app such as Data Rescue.
If you tried all these steps for a healthy drive or the drive is failing, then you should contact a professional data recovery service such as Drive Savers or Ontrack. Both vendors provide free estimates and both are recommended by Apple.
Converting a file system or enabling or disabling Filevault (or any encryption) is a bad idea because if the process does not complete, then third party data recovery apps may not be able to access any of the data on the drive (same may apply to a professional data recovery service as well). You were extremely lucky.
Always have frequent and regular backups. This applies to the main system drive as well as any external media which contains important & unique data.
