Will Fixing the Metadata Delete or Damage My Photos?
No. Writing a date does not touch the image. The pixels are untouched and the quality is identical.
Metadata lives in its own part of the file, separate from the image. Writing a date rewrites that part and leaves the picture exactly as it was. No recompression, no quality loss.
Converting formats is different, because that does rebuild the image. HEIC to JPG is a real conversion. It is optional, and off unless you ask for it.
Takeout JSON Metadata Fixer writes to a new folder by default, so your originals stay exactly where they are. It runs on your own computer and is free for your first 500 photos.