I managed to source the download links using gcd-parser (https://github.com/mbirth/gcd-parser). These are all safe links to download from as they're directly from Garmin:
19.20 Firmware & Sensor Hub 11.01.
Fenix 6
Firmware 19.20: https://download.garmin.com/gsup/006-B3290-00/19.20/full/rel/804c843c-4098-452b-9011-25346b3e402f/GUPDATE.GCD
Sensor Hub 11.01: https://download.garmin.com/gsup/006-B3295-00/11.01/full/rel/9907050e-b90e-4218-9c24-85b489f1cea1/GUP3295.GCD
Fenix 6 Pro
Firmware 19.20: https://download.garmin.com/gsup/006-B3290-00/19.20/full/rel/804c843c-4098-452b-9011-25346b3e402f/GUPDATE.GCD
Sensor Hub 11.01: https://download.garmin.com/gsup/006-B3295-00/11.01/full/rel/9907050e-b90e-4218-9c24-85b489f1cea1/GUP3295.GCD
Fenix 6X Pro
Firmware 19.20: https://download.garmin.com/gsup/006-B3291-00/19.20/full/rel/43d793ec-7959-4bb1-b3b2-ed39cb78798e/GUPDATE.GCD
Sensor Hub 11.01: https://download.garmin.com/gsup/006-B3296-00/11.01/full/rel/a6ad4724-daca-4a00-96fa-cfc2dc53beba/GUP3296.GCD
Fenix 6S
Firmware 19.20: https://download.garmin.com/gsup/006-B3287-00/19.20/full/rel/6a544f13-519a-4f21-a05a-649fb32c187d/GUPDATE.GCD
Sensor Hub 11.01: https://download.garmin.com/gsup/006-B3294-00/11.01/full/rel/e73af146-f7d0-47bd-ab9f-1a573d930de2/GUP3294.GCD
Fenix 6S Pro
Firmware 19.20: https://download.garmin.com/gsup/006-B3288-00/19.20/full/rel/a28f6971-f709-447d-9749-800a412c0268/GUPDATE.GCD
Sensor Hub 11.01: https://download.garmin.com/gsup/006-B3294-00/11.01/full/rel/e73af146-f7d0-47bd-ab9f-1a573d930de2/GUP3294.GCD
Instructions for install:
1) Plug your Fenix 6 in to your computer
2) Open up Windows or Mac file manager and go to your Garmin watch
3) Navigate to the GARMIN folder and place the GUPDATE.GCD file (firmware) in this folder
4) Navigate to the REMOTESW folder and copy the GUPXXXX.GCD file (sensor hub) in to this folder
5) Unplug the cable and it should prompt the install.
Enjoy!
EDIT: 3 minutes after this post and Garmin have publicly released the files as a sticky in this forum, what are the chances. :D I'd suggest downloading from their link rather than mine.