In case that somebody has same variant of the issue as me...

I had JObject instance that I wanted to be converted to instance of Object without keeping the information about original type. The main difference from other answers is, that I do not have any structure of the object - it needs to be variable for any structure.
The solution was to serialize it and then do the deserialization again, but not using Newtonsoft, but using System.Text.Json which created just a plain object instance. Deserialization using Newtonsoft was producing JObject again.