To be able to add Initiatives to an OKR, you need to be Admin+, be a member of the Team the OKR belongs to, be the lead of the OKR, or be made a Contributor for that OKR.
Find an overview of roles and permissions here.
You can find the Lead and Contributors of an Objective in the right side panel:
Need a hand?
Contact our friendly Support team via the in-app chat at the bottom-right of your screen, or email firstname.lastname@example.org.