Hello,
The only possible method to retrieve a variant given its barcode is by doing a GraphQL request:
{products(query: "barcode:value", first: 1) { edges { node { id } } }}
Create a product and variants ( Rest API ) then query the variant/product ( GraphQL ) using previous request it will not find the variant/product but repeating the GraphQL request in a minute would find it.
The only possible solution I see is to total convert to GraphQL which I want to avoid at this time
