HEIC covert to jpg

You can set the camera to take the images as JPEGs. You can also convert them using Preview to export them. I also managed to make this simply dragging a picture out of Photos to the desktop and it automatically delivered jpeg files (gotta check it it's a setting or just normal behavior). Please, check this: Using HEIF or HEVC media on Apple devices - Apple Support

To change the way Camera App saves media, go to Settings > Camera > Formats and select Most Compatible (only available on devices that can handle HEIF and HEVC formats running iOS 11 or later (the ones listed in the link above).

Have in mind jpeg pictures will be like twice the size of high efficiency media.

If you want to keep the HEIC version in the library export it, either in original or edited form, and set File type to JPEG.