The DD provider switched from resource_collection_enabled to extended_resource_collection_enabled a while back but in the first provider version that deprecated the former, the new resource name did not actually cause the feature to be enabled. That has been long since fixed and now, resource_collection_enabled no longer works (even though it just gives a warning that it's deprecated.
Bumped the min provider version and switched to the new var. Note that there is still a deprecation warning due to the new-ish datadog_integration_aws_account resource. This module will switch over to that soon.