We build one new website with Vaadin Flow and added to google webmaster tool. We try fetch as google. But we get following error:
I’m sorry your browser is not supported
This is known issue with Googlebot. It uses Chrome engine v41, which is ancient (2015 or so), while newest version is 67+. Read details here.
This means that Googlebot is not capable of rendering modern web apps, like those which use web components, etc. This is not limited to Vaadin 10, but almost any modern web technology framework.