Multiple Projects and One Solution - DevOps Best Practice

Question

For example, I have one solution and multiple projects. The multiple projects are:

• Solution
  • REST API Web Application
  • Admin UI Web Application
  • Shared Libraries

To have an Azure DevOps pipeline for the REST API and the Admin UI, what would be the best approach?

1. If anything changed in the solution, trigger build for everything and deploy BOTH web apps
2. CI / CD triggers for each deployable project; ie. if only UI change in Admin UI, then only build for that happens

I like #2. I am thinking that if only REST API changes, then only REST API will trigger CI / CD for itself. If Admin UI changes, only CI / CD for it triggers. If Shared Libraries is changed, both CI / CD triggers.

I believe this can be done using Path Filters as the trigger. However, what if in the future I have a new Shared Library2? I would need to edit the Pipeline trigger for that new project. So I am not sure anymore if this is good practice.