In the new objective creation experience for team objectives, there is a dropdown called "Anchor Sprint".  This field shows up, even if the team picked for the Objective is a Kanban team.

Sprints are not relevant for Kanban teams, and selecting an option from this dropdown leads to an error popup about sprints being forbidden for Kanban teams:

If a Kanban team is selected as the Objective team, please hide the sprint field completely, as it causes confusion.  Any field that results in an error after being selected should be hidden from the creation form.