Only workspace admins can edit the job owner, and exactly one owner must be assigned. The owner can be a user or a service principal. I recommend also updating run-as to be the service principal as well.
In the jobโs details panel, click Edit permissions, select the service principal, and set Owner; then Save. Only workspace admins can change the job owner.
In the workspace sidebar, open Jobs & Pipelines, select the job, then in Job details click the pencil next to Run as, search for the service principal, and Save.