We are in cloud OneStream environment and our retention policy for Non Production is 7 days and Production 365 days ( I think ). Restore from backup does whole environment restore and not application...
A single OneStream Application Database includes all its own metadata, dashboards, rules etc, including any custom table that might have been created by the customer or by Solutions.
Marketplace Solutions, like People Planning, are a set of components (typically dashboards and rules) that get loaded into an application. On first launch, they might require to create some custom tables in the Application database (or more rarely, the Framework one).
It's absolutely possible to restore an individual Application Database from the backup window. You have to request it in our ServiceNow:
This procedure will restore all tables in the Application, including any custom solution table that might exist. If you cannot find that option, contact Support and they'll send you a direct link.
If you want to restore only the state of an individual solution, i.e. only solution-specific tables (like only PLP tables), that's a custom procedure. You can discuss it with Support; it's technically doable but unlikely to give good results - those tables typically reference other elements in the Application, that might have since changed, resulting in various issues.
If you want to perform your own backups, typically as part of your development practices, you can schedule extracts via Data Management, relying on either the built-in features or custom rules. Some people use custom solutions with git, the REST api, and so on.