what are the differences between TaskPaper+ and Taskpaper (normal) syntaxes? only wiki links?
Yes, this is as per the details for the Taskpaper+ Drafts syntax in the directory.
You can also always review the content of the syntax file in reference to the Drafts syntax creation documentation.
obviously these wikilinks capability works only in Drafts not in Taskpaper app itself, isn’t it?
Yes, they are coded into Drafts and the Taskpaper app from Hogbay software only supports Taskpaper syntax.
this is the reason for Obsidian?
Obsidian is an entirely different piece of software to Drafts and Taskpaper. It supports Markdown only, It has no Taskpaper support unless it was somehow integrated via an Obsidian community plugin.