@madjedo The latest beta build of Pinegrow generates a theme.json file, which is 80% of what you’d want for block theme support. It works pretty damned well in my testing. Aside from that, there isn’t much Pinegrow could or should do other than create plaholder HTML files for the block theme.
All the heavy lifting for block themes is done by just creating blocks and adding them to WordPress. Once you have the theme the way you want it, you just use WordPress’ own export function to export the finished HTML file so you can include them in your project. (Hmm… it’s easier to demonstrate than to explain in writing…).
Regardless, there is no reason why Pinegrow can’t be used to create block themes anymore other than the fact that they suck. Sorry, was that my outside voice? (In all fairness, I’ve created a few block themes using Pinegrow for clients, and they are fine. I just recommend going the hybrid theme route since full Block Themes don’t have the customizer, and WordPress seems to think that menus should be managed as part of the theme rather than as data. That last point is on the long-term roadmap to be addressed by WP, but it isn’t likely to happen until 2024 at the earliest.
I 1000% agree that the small community is a weak spot for Pinegrow. Funny enough, that’s part of why I started making content to help get more people to use and talk about it.
For a full course on Pinegrow, their Starter Shop Course is really solid. Yes, it’s Woo-focused, but it also covers a wide range of Pinegrow and WordPress topics. Also, it’s free! Maybe @Emmanuel can add that to the Courses page in the Pinegrow documentation so I don’t have to hunt for the link each time I recommend it 
I also have my own mini-course that it specific to theme-building, but I wouldn’t recommend it as an all-in-one “learn Pinegrow” course since it focuses solely on turning a design into a Classic WordPress Theme and doesn’t include any information on how to use the design features of Pinegrow.
@Marcio For building a menu, you can very easily get 99% of the way there using nothing but the Pinegrow Interactions UI. The trickiest part is knowing which roles, actions, etc. need to be set. The WAI Example Disclosure Navigation Menu does a great job documenting all of it though, so you just need to tell Interactions what to do and where to do it. The one challenge I ran into is that GSAP doesn’t have a great way to tell when you have tabbed out of an area, meaning that submenus stay open for keyboard users until an action, such as opening another submenu or clicking a link, is taken elsewhere.