There are no scaffolders supported for this item Visual Studio 2019

Update 31/7/2019

I was mistaken (24th Update), see comments on this post, it's apparently still broken, either way, the original answer below still works, in both cases.

Update 24/7/2019

The answer below still stands if your using an older release of Visual Studio 2019, however please be aware this has now been fixed in the more up-to date releases:

https://developercommunity.visualstudio.com/content/problem/562039/there-are-no-scaffolders-supported-for-this-item-1.html

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Original Answer

There's currently a known bug in Visual Studio 2019 for this scenario.

There is some semi official advice on the GitHub issue tracker, but it doesn't always work.

MS Will fix it eventually, there appears to currently be no timescale.

For now however, if you right click and use add new item:

Then pick the item type you want (In my case it's a razor page)

Then you'll find everything still works as expected. The bug only seems to affect the shortcut menus.

I see this problem in my visual studio when I add "Pages" Folder to my ASP.NET MVC core project. before I adding this folder, scaffolding works fine, and when I add this, I see the error. Also when I remove "Pages" folder, scaffolding work fine again. ;)