You can do exactly what you’re referring to in the Field Presets for any Create and Update Permissions.
{
"populate_this_field_from_user": "$CURRENT_USER.tenants[0]"
}
If you know you’ll have a lot of folks that are a part of different teams or tenants, you could add an additional relational field on the user level for current_tenant or active_tenant or whatever you prefer the naming convention to be. You’d set that once when the user is created or added to a tenant. And then give them the option to switch to a different tenant if they are part of more than one.
The only caveat there is we don’t have a prebuilt UI component or interface for the user to “switch tenants” so that’s something you’d have to build as a custom extension.
If you don’t want to create a custom extension, you could probably also just make it a flow they could run from any collection as well in you’re using the Data Studio as the “frontend” for your SaaS users.