If I delete project in ActivityTimeline, will it affect Jira?
No, If you disable a project in ActivityTimeline it will still be available in Jira. You can make project unavailable in ActivityTimeline in ActivityTimeline Configuration→Projects→Uncheck the box ‘Is Active’:
Can I create projects directly in ActivityTimeline?
No, all projects must be created in Jira and synced to ActivityTimeline.
I created a project in Jira but it doesn’t show up in ActivityTimeline
By default, ActivityTimeline synchronizes the project list once a day. If a new project is created and you want it to be immediately displayed in ActivityTimeline, please go to AT Configuration -> Synchronization -> Refresh Projects -> and click on 'Refresh Projects':