It appears that iPhone X has uploaded my photos in new file format. How can I fix all the wrong file formats?

Are the transferred photos in the space-saving High Efficiency format? Which system version is running on your Mac?Your Mac supports the High Efficiency format, if you have have at least macOS 10.13 High Sierra or later installed.

You have three options - see: Using HEIF or HEVC media on Apple devices - Apple Support

1. Change the Settings > Camera on your iPhone to take the photos in a more compatible format and your new photos will be JPEGs. That would be the easiest way have the new photos right in the format you prefer but your iPhone will need again twice the storage for your photos.
2. Change the Settings > Photos in the "Transfer to Mac or PC" section to "most compatible", but keep the "High Efficiency Setting in the Camera Settings. The photos will be stored on the iPhone in the space saving format, but transferred to the Mac as JPEGs. The disadvantage of this is that it will disable the duplicate detection when importing from the iPhone. You will have to select the new photos manually on import and only import the really new photos.
3. If your Mac supports HEIC (macOS 10.13 High Sierra or later): Keep the Settings on the iPhone as they are, import them as HEIC files to Photos and convert the imported photos to JPEGs, when you need to share them with platforms that do not support HEIC. On a Mac with High Sierra or later you can convert HEIC files to JPEG by exporting them from Photos or opening them in Preview exporting them in a different format. If your Mac is running an older system version, that does not support HEIC you can convert the already imported HEIC files using the online converter at http://heictojpg.com/

Export the photos from your iPhone to a folder on the Desktop using Image Capture. Then open them with Preview. If you can't open them with preview you can try to use this Automator workflow/app to change them to jpeg and see if the changed version is compatible with Photos:

Safe the workflow as an application.

Just drag the image file onto the app and then try to import into Photos.

This is only for the current batch of photos because once you change the format to the most compatible as Keith suggested all future photos will be compatible.

silent2hear wrote:

Without much thought the genius at APPLE have changed the photo formats to be now incompatible with NORMAL human use.

Since I uploaded the new photos to my Mac Computer and none are useable.. HOW can I fix this?

Really silly to keep making your products incompatible with NORMAL human use!

All of that but you provided no details.

Go back to the Apple store that you went to and ask them.

It is still up to you to tell the Camera.app on your iPhone which format to use when you take photos or videos. The HEIC format needs only half as much storage as JPEGs of the same quality, so I have changed the Settings on my iPhone to use the HEIC format and have converted all previously taken photos and videos to HEIF as well. If you do not like the format, you are free to keep the Camera on the iPhone shooting in JPEG.

Change the setting in the phone to "most compatible" and you will get your jpegs back.

Why? Ask Apple - they are not here.

I really think you should sell your iPhone and Mac, and buy android/pc. I think you would have a happier life.