Subdomain product landing page setup/questions

I sell sex toys online, due to the nature of these products I am unable to advertise my main website directly. I am hoping to create a subdomain (https://try.downunderthunder.com.au) that advertisers a single product labelled as a “massager”. When the user clicks an enter button and confirms they’re over 18+, it will redirect to the main website URL (https://downunderthunder.com.au)

Is this at all possible with Shopify and if so, is anyone willing to give me some pointers. My domain is parked on a third party service and not shopify so I can’t create a subdomain from the Domain section in settings. Just not sure how to set the rest up once I’ve done that.

Any help would be appreciated and if you’re up the task of building an amazing landing page to go with it I am happy to pay you for your services.