Hello! I like features of Defold.
I learned some tutorials in Defold, Godot, practiced UE4 (not free) and Bevy (not production ready).
I would like to make Dark Souls like game.
I like that asset store of Defold has 11 Physics projects, I plan to reseach all of them.
But for full functionality, I guess, I need to create some my own extentions.
But I don’t have any experience in C++.
What I need to learn (books, WEB-sites) about C++? And how much is it hard for newbee?
Can I make game logic of different units in C++? Can I add external liblaries?
Which standard of C++ I should to learn? Which compiler I should to install for training?
What’s about the risk of the stable work (crush) of same extetions at different platforms?
At least I need to add collision shape to sword bone and animated body bones. However, I would like to add Ragdoll system and Decals System.
All of this is easy scriptable in Godot (there is internal nodes and different free extentions). So, at other forums every users recomend me Godot.
But I think that the skill of writing C++ extentions with Defold give me more possibilities for the future. So I cannot decide: go to ambitious way with C++ or easy way with C# and GDscript.
If I were learning a new game engine and/or a new programming language, I wouldn’t make Dark Souls. I’d make Pong. Then I’d gradually add more complex features one at a time. Pong with 3D swords! 
That way you can learn a little piece at time instead of having to learn everything up-front.
What makes you think this? You should be able to achieve your goals with the physics engine(s) included in Defold.
It’s difficult to say how hard it will be for you to learn C++. It depends on your prior experience, how quickly you pick up and learn new concepts and many other factor like the amount of time you spend and your willingness to try-fail-try-fail-try-win over and over again.
There are probably thousands of online resources to learn C++, books, video tutorials, interactive guides and more.
Once you are somewhat familiar with C++ as a language I also recommend that you take a look at our documentation specifically about native extensions. This page and the other pages in the same section:
Perhaps also take a look at an existing extension to understand what they look like:
Thanks. You gave me confidence in myself. I employed with not related programming work. But I know Blender, texture baking, rigging, hi-poly detail editting, normal map creating, retopology, photogrammetry as hobbyist. So at evenings I try to learn GameDev. I would like to make 3D game with my own Universe and Story. I really like that developer answer questions of newbees. I will try Defold with C++.