Steps:
- In fitler, add: no:project
- this will display all issues that are not associated with any projects right now
- then select all issues using this filter.
- click projects -> select the one to add into
To automatically add future issues to a project
- project: settings via three dots
- select workflow-> Auto-add to project
- Edit: set a rule to add all new issues to the project, any open issues from a repo