Good to find this page and I have been through it in detail. I had done everything that it listed. I posted in the comunity forums a couple days ago but as I havent had a responce I have copied it below.
With regards to your step nine, this was done a few days ago and since then Your Phone has not worked. I am currently windows 10 1909 as is my Dell Laptop. The Dell Laptop connects to the phone just fine.
Im confused as it did work last week before the repair install and the fact the phone still hooks up to my Laptop.
I have a Samsung S9+ and a windows 10 Desktop PC. The PC is wired to the router (Virgin Hub 3, UK) and the S9+ was on WiFi (same notwork) and I have been using the Your Phone App over the last few weeks. ALl working, no problems.
Last week My PC developed a couple of problems so I have just reinstalled Windows 10 (without wiping programs/apps and files. The computer is now working fine and the issues are fixed but Your Phone is no longer working.
I also have a Dell Laptop (XPS15) and that hooks up to the S9+ perfectly right now so I'm kinda sure it's not an issue with my phone.
I can't get my PC and S9+ to work as they did a week ago. I have tried everything I can think of. When I open Your Phone on the PC it shows the Galaxy S9+ in the top left and says it "need your permission to connect and access data on your phone". No notification comes through on the phone (like it can do with my Dell laptop. Hitting resend notification gives the message " We're almost done, You've successfully signed-in on your phone. Hang tight while we finish one last thing to get your device linked.
This is as far as I can get, I have tried everything I can think of. Unlinked the PC, removed the phone from my Microsoft account and readded it. I've even used the PowerShell to uninstall the Your Phone app and reinstalled it on the PC. Focus Assist is off, notifications are on on the phone. It still links fine with my laptop though