Keep in mind this is Alpha software. The stable release (my guess) is not coming until 2023, so there are tons of bugs to fix and that will be fixed. But hopefully the beta later this year will be good enough for production work.
In any case, after my experience with the Aniela demo, I've decided to start my game using Godot 4.0. I plan to take 6 months to a year to finish it, so could be a launch title for Godot 4.0. And I'll be able to report bugs with a real high end project.
So I think it is very promising, and I'm going to use it myself, but don't expect everything to work 100% right off the bat. You could always work on other things that are more important and come back to the transparent viewport issue when it is fixed.
