Trying to open original link in Illustator not working. Trying to "open with" Ilustrator from file explorer not working either. Opens Illustrator window, but never loads the file.

Seit dem neusten Update von Illustrator Beta kann man keine EPS oder Ai Dateien mehr öffnen.

I have the same issue, the only thing that works is dragging the file to Illustrator

I can confirm this happens for me as well :( Resetting Preferences does not help.

Ismail, which version specifically?

Indeed, this is something else :/
I’d start with resetting the preferences and the reinstalling it, to see if it helps (it does in many cases).
Does it help to drag-n-drop a file into the app frame / header?

In reality, it opens all types of files, but since the last update, it is unable to open Illustrator for me, neither by double-clicking, nor by "open with" and neither by selecting EDIT WITH ILLUSTRATOR in InDesign. It does open the software, but not the the file.
There is one way I succeeded by clicking in Illustrator > File > Open...
A demo file is attached

Something went wrong with your OS file associations.
What happens if you right-click any .ai file, choose 'Open with', then 'Choose another app', then check 'Always choose this app to open .ai files' and locate the Illustrator Beta in the given list? If it is missing in the list, click 'More apps' in the very bottom of it, and then 'Look for another app on this PC', to locate the proper 'Illustrator.exe' in Program Files.
Once '.ai' is associated with Illustrator Beta, it should work fine again to open documents from Explorer and with 'Edit with' in InDesign and Photoshop.

Opening Files Bug - It's not possible anymore to open files from Windows Explorer Window or from InDesign (edit with ... ) Opening files only possible by going through Illustrator itself - "Open ..."