I just checked and yes it's possible to use Webhooks with a Mongo DB (using their Cloud service)
Just go to Integrations and add Webhooks, there you can configure them however you want.
Links:
https://supabase.com/dashboard/project/%7Byour-project-id%7D/integrations/
then it's available at
https://supabase.com/dashboard/project/%7Byour-project-id%7D/integrations/webhooks/webhooks