Recover the date a photo was taken
A photo carries two different dates, and Windows shows one or the other depending on the view. That explains almost every sorting problem.
Two dates that get confused
The modified date comes from the file system and is reset every time you copy something. The date taken lives inside the photo itself, in the capture data, and was written by the camera. Only the second one is what you mean when you say sort by date.
Why it disappears
When converting, the capture data does not travel by itself: the tool has to write it into the new file on purpose. If it does not, the value is gone. Messaging apps strip it on sending too, deliberately, for privacy.
What can be saved
If you still have the originals, nothing is lost: convert again with a tool that carries the date across. If only the converted files remain and the field is empty, the date cannot be reconstructed — it is not stored anywhere any more. All that is left is typing it in by hand, under Properties › Details.
Convert HEIC photos to JPG — right in your browser
Switch off the wifi before you start if you like. It keeps working — the conversion happens inside this window.
Select photos