The 1mm or 0.040” restrictor is pretty much the standard Garrett recommendation for ball bearing turbos when you have 40 to 45 psi oil pressure (2.75 to 3.1 bar) at the turbo.
https://www.turbobygarrett.com/turbobygarrett/oil_restrictor
It is not normal for journal bearing turbos to require external restriction. They can tolerate a pretty wide range of oil pressure. The Garrett carbon face seal is a little more sensitive when the pressure behind the compressor wheel is really low, but this is something we induced in the lab. I doubt it can happen in the real world. On the other hand, restricting journal bearing pressure at the turbo oil inlet also cuts the oil flow to the turbine side, which makes it run hotter than it already does.