How to use OR / AND in graphql query filter or make a case insensitive filter?

Currently there is not anything built-in to graphql itself that uses case insenstive search, its completely based on whatever library the graphql server is running and if that chooses to add support for that. If you can modify the graphql query code, you can add that in yourself in some fashion, or request whoever is hosting/building that to add in that feature somehow.

Regarding OR, I doubt I could say it better than https://github.com/graphql/graphql-js/issues/585#issuecomment-262402544

GraphQL doesn't have support for AND/OR operators for exactly the reason you mentioned at the top of your issue: it does not map to any kind of storage. I think to properly understand why it does not have these requires a shift in mental models. We think of GraphQL as more similar to RPC languages than database languages.

To help understand the mental model shift, it's useful to think about fields and arguments like function calls in programming languages. So suppose we ask a similar question of javascript: Why can't you type: getCaseByStatus("open" OR "closed")? The answer, I would assume, is because JavaScript does not know what OR means in this context. Should the values "open" and "closed" be combined in some way to produce another value? Should the execution of the function getCaseByStatus change in some way? JavaScript can't be sure - because the concept of field-based filtering is not part of JavaScript's semantics. ...

Does regex work? Something like

  allMarkdownRemark(filter: { brand: { 
     regex: "/($normalBrand)|($normalBrand2)|($normalBrand3)/" 
  } }) { 
        edges {
            node {
                webImages {
                    url
                }
            }
        }
    }