TLDR: If you know what you are doing and just can't get your maps to load:

1. Source overlay image must be less or equal to 1024 x 1024

2. Source overlay image must encoded as Not Progressive

Software

This guide will allow you to load custom satellite maps on your Garmin Fenix 5X with free software. In order to do this, you will need the following:

Gimp for editing images

Google Earth Pro

Thats it!

Google Earth Pro

Open google earth pro

Under "Layers" turn off terrain, and other features if you do not want them in your final map

Select the Save image icon, and be sure your resolution is no more than 1024 x 1024 .

icon, and be sure your resolution is no more than . Anything above 1024 x 1024 will cause the map not to render on the device.

Turn off all the map options

click Save Image

I will call my image copper.jpg

Gimp

Open Gimp

Open your image, in my case copper.jpg

Go to File then Export As

then Then click Advanced Options

Make sure Progressive is Unchecked otherwise the Garmin unit will not load the map. Override your old image

Back to Google Earth Pro

Back in google Earth, Click the Add Image Overlay button

Set the Name

Select the image you just exported

you just exported set the transparency to around 50%

to around Don't close this window yet! Just move it out of the way.

Align your image. At first it will be out of alignment.

Once it is aligned you are done, you can click Ok to close the image overlay dialog.

Right click on your new place and Save Place As

Save as type kmz

Upload to GPS

This is the easy part.