I am trying to assign default value to standard story point jira field (i.e. non-custom field) on creation of issue in a specific project. Is there a way to do it?
Now when each issue is created, it will add the desired default label as long as the issue is created in that project. You might need to refresh the page after each issue creation to see it.
You can do this via global rules to apply to all projects also. You'll need to be a Jira Admin/Site Admin, then instead of going to Project Settings, go to Jira Settings (cog icon on left-hand navigation bar) > System > Automation Rules (left-hand menu).
For more on using Automation For Jira see these help pages.