Earlier, All add-ins and SharePoint Framework Solutions had to be managed centrally in the tenant app catalog. A deployed package was visible on all site collections. There was not specific way to deploying add-ins or solution only to specific sites.
Now tenant administrator can enable app catalog on the specific site with the site collection app catalog feature. Once you enable to app catalog for a site collection, administrator can deploy the add-ins and solutions packages and which will be available only the specific site collection.
How to enable site collection level app catalog?
Enabling site collection level app catalog required tenant level administrator role.
Download and install SharePoint management shell.
Connect to the Tenant
Connect-SPOService - Url https://companyname-admin.sharepoint.com -credantial email@example.com
Connect to the site and enable app catalog
$site = Get-SPOSite https://xyz.ssharepoint.com/sites/appcatalogsite
Add-SPOSiteCollectionAppCatalog -Site $site