After you mark an activity as done, you will automatically be prompted to create another activity for that specific deal, due to Pipedrive's activity-based selling design. However, if you use the Workflow Automation feature to automatically schedule activities for you, this can create duplicate follow-up activity efforts.
If you have any active Workflow Automations, you will be able to disable these popups by going to Company Settings > Activities > Show activity popup. From there you can disable or enable these follow-up activity popups. If you choose to enable them, you can choose to always have them enabled, or only enabled on certain Pipelines.
If you are on the Essential plan or don't use the Workflow Automation feature, you will not be able to disable these popups.