Well, there are other T trainings there, e.g. T200, T210, ..., T280. 

In my opinion it's a good start.

https://openuni.acumatica.com/learning-paths/developer-learning-paths/development/

I have to agree, the T200 series on Acumatica’s open university are a great way to get you on your feet. Then for more advanced tips & tricks as well as learning about Acumatica best practices I find the Acumatica Developer’s Blog to be an invaluable resource: https://asiablog.acumatica.com/

That resource isn’t structured to teach you from the ground up, but it’s super useful to teach you specific techniques that are commonly used.

Also, you can find structured list of learning resources here:

https://www.acumatica.com/developers/onboarding-new-acumatica-developers/

I also recommend you to join the Virtual Dev Conf

https://www.acumatica.com/acumatica-virtual-developer-conference/

Wow - “learn the whole framework” might be a bit more than you think!   Some of us have been working in it for years and still learn new parts of the framework regularly as our understanding depends.  I’d suggest aiming for a basic understanding first and then dig deeper.  In my opinion, you should break up your learning objectives into 3 areas.

1. The basics - Making a Customization Project, screens, graphs, DAC’s, methods, and events.
2. Web Services - How to talk to Acumatica from another Acumatica instance or external applications
3. Mobile Development - How to configure new or existing screens in Acumatica for the Acumatica Mobile App

Acumatica is built in C#, so the first step is to determine if you need the prerequisite training.  If you need to learn C# basics first, here are a couple of places to start:

• C# docs - get started, tutorials, reference. | Microsoft Docs
• C# Fundamentals for Absolute Beginners | Microsoft Docs

Once you have the basics there, you can move into the resources (including Open University courses) mentioned by others in this thread.  As Dmitrii mentioned, links to your best official resources are found at

• https://www.acumatica.com/developers/onboarding-new-acumatica-developers/

Complete the developer training courses… do them all, start to finish, and don’t cheat by using the source code they provide and doing copy/paste.  I find that retyping the code as instructed involves more senses, so you retain it better.  Some of the basics like simple syntax will be absorbed this way through repetition.

Once you complete the first training course, you might check out some of the early posts on my blog site where I tried to document some the things that I struggled with or just wanted to do a brain dump from my early days.  It isn’t an official Acumatica site, and some of the content is growing outdated as we upgrade through the years, but the basics generally will stay the same.

• Brian’s Blog – Acumatica.dev

I also highly recommended Yuriy Zaletsky’s blog where I found a lot of useful information.  Yuriy committed to documenting things that took him a bit of time to figure out, so it’s full of lots of great content.  (He inspired me to start my blog in a similar way.)

• Blog of Yuriy Zaletskyy | Anything that takes more then 15 minutes to find out I put here

Finally, and this may be the key to it all… get heavily involved in the developer community.  People post questions on Stack Overflow (tagged Acumatica) and on here.  Try to answer what you can.  If you think you have an idea, but you don’t know exactly how… research it, try it, and then give the solution if you found one.  This methodology is how you grow beyond the confines of your own environment.  It exposes you to ideas from others on tools and techniques that you won’t get on your own.  You only truly know something when you know it well enough to explain it to someone else, and this strategy gives you virtually limitless opportunity to do just that.  In so doing, you will solidify your knowledge in the basics and advance your skillset beyond the average developer.