I hope you don’t mind me posting this as it’s really an iPhone issue? I took some photos on holiday with my iPhone 12 and wanted to load them on a USB stick to view on my TV. I noticed they were in HEIC format and correctly guessed my Panasonic TV couldn’t read them. Opening each image in Preview I could export them as JPG. I noticed there was no JPG suffix at the end of the exported file, just a number, but the TV could read them ok. I had nearly 200 photos though so I wanted ideally to batch convert them. I did this on my iMac but two things were different. The first was that it gave all the images a JPG suffix BUT also indicated that the average file size would be around 2.4MB. Exported individually each image was 7.1 to over 13MB. In the end I exported individually to be on the safe side. If I’d batched them would the images have been of lower quality? I didn’t see the option for “best” when batching, but did see and chose the option exporting individually. The pictures came out extremely well and I’m now wondering why I’m carrying a MILC and two lenses on holiday! 
