How to build job only when certain files in a folder are changed?

Hello, I currently have a monorepo setup and in the .yml file, I only want to build the jobs where there are changes in certain files inside of the folder I’m targeting

For each job, I added “rules” to check if a file has been updated only if the commit is a “merge request”
or is pointing to the default branch.

This is what I have so far in the rules for the build job:

- if: ‘$CI_PIPELINE_SOURCE == “merge_request_event” || $CI_COMMIT_REF_NAME == “default”’
changes :
- app1/src/** /*

The pipeline successfully builds, but it adds the build job even if there are no file changes inside of the app1 folder.