If it's useable in content blocks, shouldn't this at least be documented? It is also useable in landing pages, also not documented.
Documentation seems to be lacking in other regards as well, I don't see the ability to access workflow context described anywhere, although it can be done (using $(vars/@parameterName) as in Classic).
Using JS is not allowed in ACS, neither in workflows, landing pages, content blocks.
What you are referring to might be possible in the product, but will not be supported and can lead to issues/errors when upgrading to a new version. For that reason, you cannot find any documentation on this.
Where in the documentation is it stated that it is not allowed?
In the documentation for content blocks (https://helpx.adobe.com/se/campaign/standard/designing/using/adding-a-content-block.html) JS is used without any indication that it wouldn't be allowed. There are also posts in this forum by Adobe staff where they refer to using JS as a solution to different issues.
Can someone answer that, is there any possibilities to use the JS activity/support for some customization in ACS with Adobe's help?
As, there are some JS activities are running in some technical workflows in ACS so likewise, can we use with Adobe's help to do the customization in future?