Is it possible to send an account invite to a customer using GraphQL API?
I couldn't find any documentation or examples for this.
There is no alternatives to the REST API endpoint available for GraphQL. And besides, GraphQL is more about queries/mutations, rather than actions like sending emails.
If you use storefront graphql API's, as soon as you create an account using the mutation "customerCreate" an account activation email is send. - https://shopify.dev/docs/storefront-api/reference/mutation/customercreate?api[version]=2020-04
The downside is you don't get to add tags or metafields using this mutation.