Yes, this is Gilbert syndrome. Here's my beef with this question: UDP-glucuronosyltransferase is a liver enzyme. Conjugation takes place in the liver, not the serum.
Here's how you can diagnose Gilbert syndrome according to UTD: "A reduction in hepatic bilirubin-UGT activity, which is approximately 30 percent of normal" https://www.uptodate.com/contents/gilbert-syndrome-and-unconjugated-hyperbilirubinemia-due-to-bilirubin-overproduction
Here's a picture from UTD of the enzyme sitting HAPPILY WITHIN THE HEPATOCYTE: https://www.uptodate.com/contents/image?imageKey=GAST%2F52393&topicKey=GAST%2F3578&search=gilbert%20syndrome&rank=1~53&source=see_link
So how is this a "deficiency of serum glucuronosyltransferase"?
Meanwhile, according to FA2020 p394, Gilbert syndrome also causes "impaired bilirubin uptake." Aka "Impaired hepatic storage of serum bilirubin"
My rage knows no bounds.