My Real-time preview doesn't work in any browser.

It is an awful, glitchy feature, turn it off by going to preferences => real-time preview and check 'default to static browser preview

I intentionally disabled Real-Time Preview because it doesn't play nice with my local testing server. 

Go to Preferences > Real-Time Preview and check the box for Default to Static Browser Preview.

The preview on device feature has been discontinued as of Nov of last year so that explains part of your error: https://helpx.adobe.com/dreamweaver/using/device-preview.html .  However, if you are not able to preview in browser, is your testing server running?  Also, as you are using a non-standard port could a firewall be blocking access?

There might be an issue with your connection to Adobe's servers. It may just start working later.

For me, real time preview and the device preview QR (what you're showing in your first screenshot) have never worked the way they were intended. For that reason, I use a local testing server which allows me to preview the site from any device connected to the same network and Static Browser Preview which is essentially the old version of Preview in a Browser. 

You can change your setting for browser preview under Edit > Preferences > Real Time Preview then check the box for "default to static browser preview" at the top. That will take Adobe's servers out of the equation and show your local file in your browser without running it through Adobe first.