Aris got too much wrong on this, but could explain why the differential-behavior in ACC was so very wrong for many years and still differs from rF2 and other titles. Not the locked, but with the open differential
the torque-split is always 50/50, but this is certainly not giving you oversteer on power in high-speed-corners, because the outside wheel has more friction and more travel to accomplish and so demands more power and torque. LSDs provide better cornering capabilities because once the lateral grip changes to the outside wheel so does the torque on throttle. An open diff still provides half the torque to the inside wheel that demands only a fraction of it.
A locked differential only provides a 50/50 torque split if you drive completely straight with matching lateral grip. If one wheel is stuck and the other in the air, the torque split is 100/0 obviously and that's why they are so powerful in offroad conditions. With an open diff it's still 50/50, but if the friction is 0 on one wheel (in a perfect world without internal friction and mass intertia of components), there is 0 torque applied and so 0 on the wheel that's stuck while the power just heats up the engine, components and spinning the free wheel.
The preload (screw) is just the value of how much both diff-sides are locking together with the wrench. It provides stability in high-speed corners, but that doesn't mean understeer. Open diff cars can easily snap oversteer off throttle during corners, but that doesn't mean they oversteer in fast corners. They can only oversteer while lifting and coasting and happens in slower and fast corners.
To my knowledge GT3-teams can change the internal differential clutches as they like, but it needs to be disassembled completely, so can't be done on the fly during testing unlike the preload. But it can be done between the days on race-weekends and cars like the Porsche GT3 R in rF2 doesn't even allow preload-changes, which is BS. I even saw a video how they changed the diff-plates and preload in the Porsche GT3 R, but it got deleted or can't find it anymore.