I have a template for a plan that my team uses for new events all year around. I need a way to duplicate this Planner plan as a new Planner tab in Teams.
Using Planner's own Copy/Duplicate feature will create a NEW group and a new Team.
Looking at Microsoft Teams and Planners UserVoice I can see that it is currently not possible:
The online planner website now has the option to select the group to copy plans to. That also allows to select which parts of the plan you want to carry over.
Simply go to https://tasks.office.com/ click the three little dots on the "template plan" and select copy plan.
The script above is still (as far as I know) the only way to copy a plan within the same team directly from Microsoft Teams.