Getting a JObject by a property value
Not being able to use POCO is tough enough so don't make your life even harder with the line you're asking about. It's much easier to query it with JsonPath like that:

return (JObject)relationsJSON.SelectToken($"$.Relations[?(@.Name=='{relationName}')]");


and since you are not using POCO then you don't have to deserialize it. It's ok when you just let json.net parse it with JToken and then do the JsonPath thing:

JToken.Parse(json).SelectToken(...);