Hi M,
Thank you for reaching out to the Google Ads Scripts support team.
It is not possible to get the targeting information of Performance Max Campaigns via its selector. Our documentation may be used as reference for the available methods that could be done with said campaign using it's selector. What could be done instead to retrieve targeting information on its ad schedules is by reporting, wherein a campaign_criterion report could be created filtered on campaign.advertising_channel_type of PERFORMANCE_MAX. I would recommend you follow the blog post for further updates on this feature.
I hope this helps! Feel free to contact us if you still have any concerns.
Thanks,
Google Ads scripts team