Why cannot use "many-to-many" in relation with User from admin

System Information
  • Strapi Version: 3.4.5
  • Operating System: Ubuntu 18.04.3 LTS
  • Database: SQLite
  • Node Version: 14.15.4
  • NPM Version: 6.14.10
  • Yarn Version: 1.22.10

Why can’t I use other types of relationship with the User (admin) entity? I can only use one-to-one and one-to-many