Usually, the goals for the vision and the company are set by the management.
Team leaders should define most of the objectives, whereas team members should contribute to defining most of the Key Results.
OKRs work when team members feel that their ideas in creating Key Results contribute to the goal. A bottom-up approach is a key to commitment and alignment.
Team leaders develop and deliver objectives as context at the outset of the OKR drafting session. The leader frequently asks for feedback from team members even before the start of a workshop. Consequently, by drafting the objective, the team creates the main outcomes. Some leaders remain in the workshop but delegate process governance to the team. Some prefer to present the workshop's objectives and explain "Why now?" before leaving. They may return later to discuss and complete the drafts together.
How you approach depends vastly on your reason for introducing OKRs in the first place.