Visual Studio 2017 xaml designer not available

In the Visual Studio 2017 Installer, I selected all of the SDKs and installed the missing ones. This did not fix the problem by itself, but a subsequent 'repair' from the Visual Studio 2017 Installer (available from the 'hamburger' drop-down) did.

Sometimes, adding or removing SDKs from the Installer toggles the 'Enable XAML Designer' check box under Tools -> Options -> XAML Designer -> General (or perhaps it was the repair step that turned this back on), so ensure that this is checked.

Frankly, your situation is different than mine. In my situation, it was because of Resharper. Maybe this may useful for someone else. What to do is checking Resharper Options > Enviroment > Performance Guide > Disable XAML Designer.

It must be set to "Ignore" or "Show in Status Bar". Otherwise, it will always disable XAML Designer.