If your internet connection drops and router needs to be rebooted you have a bad router/modem. You should not be able to cause that by anything on your local network. Looking at Sky fibre's webpage it appears that they only offer 1.2 Mbps in upload speed. So it is much slower than the download speed which is pretty typical for cable based internet. At that rate, a single raw file (say a 30MB raw file) upload takes 200 seconds, so it will take an incredibly long time get all your files up even if you are able to saturate your internet connection. If uploading anything for a while crashes your internet it typically means your modem is underpowered.
Are you sure you wanted to install Lightroom CC and not Lightroom Classic? Lightroom CC is a completely new program that Adobe just released that they very unfortunately named exactly the same as the Lightroom we know and love. They renamed Lightroom into Lightroom Classic and updated it at the same time. Many people are installing Lightroom CC thinking it is an upgrade from the previous Lightroom. It is NOT! It is a new app that stores all your images in the cloud and misses 90% of the features that the Lightroom you know had. If you don't want to wait a month for your images to upload, and want to use the features that Lightroom needs such as being able to print and much more, just use Lightroom Classic. The differences are explained here: https://www.lightroomqueen.com/lightroom-cc-vs-classic-features/
My router is in perfect working order but this upload is freezing my internet on all other devices. My upload is 10 Mbps.
Yes I wanted to install Cc I was aware of the difference and had just upgraded my account. You are wrong about Sky my upload is over 10mbs. I have persevered and manged to sync all my pictures and it is working OK now.
"upload is freezing my internet on all other devices"
This is very typical for a standard type of router that doesn't do QoS on an asymmetric connection. Nothing wrong with that just that it isn't made to make sure to sustain good service for everybody else when one upload is hogging all bandwidth. Normally that is not a big deal but when you need to upload 100's of gigs it can be an issue. Routers that do QoS will ensure you other devices still get bandwidth even if one computer hogs the upload.
"You are wrong about Sky my upload is over 10mbs"
That's great. When I answered before I had taken a quick look at their website and didn't see any plans with an upload over 9.5 mbps. That seems to be the very fastest that they offer in their special max package: "Sky Fibre Unlimited Plus – with download speeds of up to 52Mbps and upload speeds of up to 9.5Mbps.". Their normal plans are only 1.3 Mbps upload. This is the first link that comes up when I google sky fibre. Your provider could be a totally different Sky as that is a rather generic name of course.