First, define the terms.
Offshore is a tax-free territory
An oligarch is a rich man who influences decision-making on a national (regional) scale
We are a large country with a fairly large population and traditions of a welfare state - it is difficult to refuse to collect taxes throughout the country, because there are obligations. But there are territories that are exempt from certain taxes.
We have oligarchs - people who are not formally part of the state system, but who have influence on decision-making by power structures.
I think that the answer to this question is not easy.
All these schemes are hidden by those professionals who should, in theory, be engaged in their disclosure. So, it will be possible to understand where the money has gone and who owns it now only after the investigation, and now, unfortunately, it is not possible.