HEIC (High Efficiency Image Container) is the photo format Apple uses since iOS 11. It uses HEIF encoding, 50% smaller than JPG with the same quality. The downside is poor compatibility.
Uploading to social media, sending to Android users, editing on Windows, printing — all need JPG format. Use a HEIC to JPG converter for batch processing.
Settings → Camera → Formats → Choose "Most Compatible" (JPG) or "High Efficiency" (HEIC). Choose JPG if you share photos frequently.