Click either in the get started dialog or on the ‘New template’ button
Specify if you want a custom or Jira native project template
2.1 Custom templates are initiated by selecting a base project that the template settings are based on.
You can customize the template settings later individually.
...
2.2 Select Jira project type ‘Software development’ or ‘Work management’ and specify further which native template you want to base the template on.
You can customize certain template settings later, even some settings for Jira native templates.
...