How does it know which quality to use?

It runs a binary search: it tries several quality levels and keeps the highest one that stays under the target size.

Is the camera data lost?

No: capture date, camera, lens and GPS are copied into the WebP. Only the embedded thumbnail and the maker notes, which are large, are dropped.

Convert camera photos to WebP, automatically finding the quality that brings each photo to about 300 KB, without losing EXIF data.

1Drop in your photos or a whole folder.
2The «Camera photos» profile resizes to 2560 px and finds the quality that gets closest to 300 KB.
3If you need a different size, edit the profile and change the target in KB.

How does it know which quality to use?: It runs a binary search: it tries several quality levels and keeps the highest one that stays under the target size.
Is the camera data lost?: No: capture date, camera, lens and GPS are copied into the WebP. Only the embedded thumbnail and the maker notes, which are large, are dropped.