Sign In button grayed out TeamViewer 14.1.9025 - SOLVED
I'm posting this because I did a bunch of searches and none of the results fixed my problem. The problem is the Sign In button was grayed out and none of the suggestions worked and I was on the latest version. The answer was so basic, I had to slap myself. However having it turn up in a search would have saved me a lot of time and frustration.
I had a VPN Proxy running which breaks TeamViewer (of course). All I had to do was turn it off.