Sharing Bitbucket Pipelines configurations between repositories is something that has been desired and requested for a long time.
Up until August 2023, it was straight up impossible (as you can also read in this SO post).
Then, in March 2023, Bitbucket stated in the community form they were working on this feature and tracking it in this Jira issue: BCLOUD-14078: Sharing pipeline yml files.
Finally, in August 2023 it's possible, but only for the Premium Plan: