I installed a dictionary under the newest ipados and since then I‘m not able to deinstall the app. I tried already using the deinstallation over the manager of the ipad-storage under the general settings but there isn‘t even the button for deinstalling apps, even if I choose another app. Do you have a hint except erasing the ipad and renewing the system?
Based on the comments, I think this is related to Screen Time.
Assuming you're the owner and don't want Screen Time on or that it was turned on by mistake, simply go to
Settings -> Screen Time -> Content & Privacy.
iTunes & App Store Purchases. Make sure the setting for 'Deleting Apps' is 'Allow'.
From there you can back out and leave the rest of the settings as-is or turn off the restrictions. To turn off restrictions, turn off the 'Content & Privacy Restrictions' switch. You might be prompted for your password or PIN to do this.
The image below is from an iPhone but the flow and look are similar to the iPad.