Hi Herbert,
Thanks for posting in the community. We are happy to help you.
I have tested it on my end and can reproduce the same situation. Currently, the new Planner app doesn't display the three dots of the plan. I haven't found any settings that can control this situation. As a workaround, you can go to Planner for the web (https://tasks.office.com/) and go to this plan to see the three dots.
If you still don't see the three dots of the plan in Planner for the web, please point it out and let us know. We will keep on assisting you.
Based on the situation, I suggest you click the More button next to the Share button> Feedback> I Don't Like Something. It's the platform for us to hear your voice and improve our products.

Sorry for the inconvenience that happened to you. Appreciate your understanding and patience.
Sincerely,
George | Microsoft Community Moderator