This is a serious problem for stolen artworks. Back in the day the IRA stole several. The most use they ever were was as collateral to other illegal organisations. If you can find a decent history of them, it’s fascinating but the long and the short of it is that even to a large, well connected organisation they just proved more trouble than they were worth,

The truth is, the aesthete billionaire collector beloved by movies doesn’t much exist. Most truly expensive artwork is bought either as a store of value or to show off. Both require you to be able to publicise you have it.