This looks like a bug / permission issue when Opportunity Owner Decoupling is ON.
Setup:
  • Leader = Contact Owner + Opportunity Follower
  • Agent = Contact Follower + Opportunity Owner
  • Leader permission = Restrict data visibility to only assigned data is ON
Issue:
The Leader can view the opportunity, but the Opportunity Owner dropdown is greyed out and cannot be changed.
This prevents the Leader from reassigning the opportunity to another agent, even though the Leader remains the Contact Owner and Opportunity Follower.
Expected behavior:
If the user is the Contact Owner and/or Opportunity Follower, they should still be able to change the Opportunity Owner when Decoupling is ON.
This is important for teams where Leaders handle lead reassignment and distribution.