When you associate the Power Platform environment with a security group, only the members of security group will be added as "Users" for the environment. You can see the "Users" from environment details page:
From the Microsoft Power Platform admin center, select the environment to which you want to add users.
Select Settings > Users + permissions > Users.
Source: Add users to an environment
You'll see the list of users that have already been added to the environment.
- If a security group is associated with an environment, only users with Dataverse licenses or per app plan that are members of the environment security group will be created as users in the environment.
- If you don't specify a security group, all users who have a Dataverse license (customer engagement apps such as Dynamics 365 Sales and Customer Service) or per app plan will be added to the new environment.
- All licensed users, whether or not they are members of the security groups, must be assigned security roles to access data in the environments. You assign the security roles in the web application. If users don’t have a security role, they'll get a data access denied error when trying to run an app. Users can't access environments until they are assigned at least one security role for that environment.
- Control user access to environments: security groups and licenses
- Create and manage environments in the Power Platform admin center
In your case, if only the admin-group is associated with the environment then only the members of admin-group will be added to the environment. Then you can share the Power Apps applications and Power Automate flows with the users of admin-group.
If you want to add other group members to the environment, you should be able to do it manually by following: Add users to an environment