Add UseAccessRequestDefault Rest API or CSOM when receiver is the team site owner in Access Request Settings.
There is a new option to allow the team site owners to receive the access requests email, but there is no Rest API/CSOM to support this, Please have add this into CSOM API, Thank you.
Nick Krieble commented
This is pretty important to us (48k E1/E3 licensed customer). We need this capability to support a lot of our internal project tools - they are all heavily dependent on creating sub-sites in a site collection with no quick roadmap to change that. Our biggest gap at the moment is the Sharing mechanism is broken to set this to match our needs.