Think there is some confusion about what you are wanting to do due to how you are describing what you want.
There can be different types of environment (e.g. Sandbox, Trial, Production)
Each Environment is a Dataverse.
Each Environment is also often referred to as an Instance.
Each Environment has a set of Tables, standard out of the box ones (like contact, account and activity types) and can have custom Tables.
All of your environments are in your Office 365 Tenancy and part of the Power Platform functionality.
By default Power Automate Flow is tied to an environment (however, if using the Default environment - not recommended - can be some differences).
To move things between environments (e.g. Dev->Test->Prod) package things in a Dataverse Solution, export it and then import it into the target environment (or use Pipelines). Technically Flows also have their own Solution concept, but is generally better to use the Dataverse Solution.
To move various data between environments use the Configuration Migration tool (or standard Data Export/Import.)
Technically there can be differences between the different environment types e.g. a Developer environment less storage. A Sandbox environment is essentially the same as a Production environment functionally but technically runs with less Application Servers than a Production Environment, and the retention period of the backups is less.
Most will have at least: 1 Sandbox as their Development, 1 Sandbox as Test, and 1 Production as the Production environments. If you have multiple Development environments you need to spend more time and have an environment to 'stage' things prior to moving to Test environment (to ensure work from multiple environments doesn't have clashes)
