I'm Java backend engineer and would like to start the brand-new project. Unfortunately for me working with UI is some kind of nightmare :) This is why I'm looking for some framework which will abstract me from the low level JavaScript details and the best choice for now looks like is Vaadin Flow (pure Java).
Right now, I'm trying to select - what is the right version of Vaadin to start the project with - Vaadin 14 or recently released Vaadin 20? Please advise. Is it the right time to start with Vaadin 20?
It depends when you want to go to production with your application.
You can checkout the Vaadin roadmap to see when the releases are planned: https://vaadin.com/roadmap
Upcoming releases
If you want to go live next year I would go with Vaadin 20 otherwise with Vaadin 14.
In one project we are on Vaadin 20 already because the DataProvider changed in 19 and you don't need a CountCallback what is very handy if you want to use Grids with data from a REST API where you never have a count endpoint.