Hi @Rainer Bünte,
Thanks for sharing the screenshot. Since toggling GPU Performance didn’t help, could you please try resetting Illustrator preferences and check if the cursor becomes more visible after that? Also, let me know if the problem shows up in every file or only in certain documents. Are you using a custom workspace? If yes, try creating a new one and see if the issue persists in that.
Looking forward to your update.
Abhishek