Since August 2023 including a pipeline from another repository is now possible, but only in the Bitbucket Premium Plan.

See this Atlassian Blog article from Aug 24, 2023: [New Premium feature] Share pipeline workflow configurations across your repositories

I've written a more detailed answer on a more recent SO question about this with more context.

To check if the feature is still Premium only, visit Bitbucket's Pricing page and check which plans include the "Scale CI workflows" Core Feature.