Managed to get it working. Documenting the steps for others. If there is better way, please do let me know

1. Running Minio locally at 9000
2. Have the Client created as follows

iex(1)> client = AWS.Client.create(“id”, “key”, “localhost”)
iex(2)> client = %{client | port: 9000}
iex(3)> client = %{client | proto: “http”}
iex(4)> client = %{client | endpoint: “localhost”}

#AWS.Client<
  region: "localhost",
  service: nil,
  endpoint: "localhost",
  proto: "http",
  port: 9000,
  http_client: {AWS.HTTPClient.Hackney, []},
  json_module: {AWS.JSON, []},
  xml_module: {AWS.XML, []},
  ...

Then used it to invoke

iex(5)> AWS.S3.create_bucket(client, “mybucket”, %{})

{:ok, nil,
 %{
   body: "",
   headers: [
     {"Server", "nginx/1.19.2"},
     {"Date", "Tue, 03 Oct 2023 22:30:21 GMT"},
     {"Content-Length", "0"},
     {"Connection", "keep-alive"},
     {"Accept-Ranges", "bytes"},
     {"Location", "/mybucket"},
     {"Strict-Transport-Security", "max-age=31536000; includeSubDomains"},
     {"Vary", "Origin"},
     {"Vary", "Accept-Encoding"},
     {"X-Amz-Id-2",
      "e0c385c033c4356721cc9121d3109c9b9bfdefb22fd2747078acd22328799e36"},
     {"X-Amz-Request-Id", "178AB98C4ABCE5E0"},
     {"X-Content-Type-Options", "nosniff"},
     {"X-Xss-Protection", "1; mode=block"}
   ],
   status_code: 200
 }}