p5.js, C#, C++, Unity, and Godot.

i second this 👍

In general, I think KA is trying to do too many different things and not doing most of them well.  I wish KA would focus on fixing and improving their core competencies rather than adding new things when they don't even correct the existing courses (such as a key word in captions & transcript that I reported over a year ago that still hasn't been fixed).

First, my understanding is that making their IDE work with a particular version of processing.js is a lengthy and expensive process.  They made mistakes in the current IDE that are frustrating and still haven't been fixed (despite being reported many years ago) -- my guess is that they would also make mistakes if they made an IDE to work with the current processing.js.
Next, I see no point to KA adding an option to use a version of processing.js that they don't teach -- at most, they could add an article with suggestions for other places to use the most recent version of JS & processing.js (but I doubt they would, since that might encourage learners not to rely on KA for everything). 
In order to teach the newer version of processing.js, they would need to remake most or all of the videos and articles in all JS Units (1, 4, 5, 6, I think).  Since KA no longer has the ability to make or change walkthroughs, they would have to use a different method of teaching, such as what they did with Python (a video shows the programming, and the video has a single linked program -- rather than being able to pause the program and play with it at any point in the process).  Making the videos & articles for a course is a very long process: it took Khan Academy several years to add the Python course -- several years before any of it was uploaded, and I think about 2 years from when they started uploading until Unit 7 was fully uploaded.
I also hope KA gives users many months' warning if they ever take away the current version of processing.js -- the programs that many people worked really hard on would stop working.

I think it's great that you want to learn C# and C++.  Maybe you can find free online platforms that teach them, or maybe other users can suggest some.

~ Janice, KA user since 2014

thx for the comment, but i dident say they should delete the old one, just add the new one and why couldent they make more talkthroughs?

I was told by KA staff that they can no longer use the software that they used to make the walkthroughs.  (Maybe they no longer have a license to use it, maybe it doesn't work with the latest operating systems, maybe the people who knew how to use it no longer work for Khan Academy, ...)

Did you read what I wrote about what it takes to "just add the new one"?  Did you understand that it's probably thousands of hours of work?
Even if they put in that work to add the new version, what's the point of doing that if they don't teach the differences in syntax so people can use it?  How many hundreds of hours of work would it be to add a unit for that?