The Modern DFFS is developed as an SPFx solution for the Modern SharePoint on Microsoft 365. It is installed as any other APP in the App catalog by uploading the app to the Apps for SharePoint library in the Tenant or in the Site Collection.
If you are the tanant admin you can add it to the Tenant App catalog and make it available for all site collections in the tenant. If you don't have the nessecary rights, you must ask your IT department to set up a Site Collection App Catalog in your Site Collection so you can uploade it there.
You can refer to this article from https://learn.microsoft.com/
The file is compressed so you must unzip it after you have downloaded it to your computer.
Browse to your App Catalog, upload dffs.sppkg to your Apps for SharePoint document library and activate by checking the Make this solution available to all sites in the organization checkbox.
The DFFS button will now be visible in the banner on all lists and libraries for users having manage lists permission.