@RedRevNow I assume you're going off the Engine Braking - EB rotary that the steering wheels often have? I don't think we ever got a proper insight on how those work - as usual, when it comes to anything F1 tech! But there's at least two ways for that to work.
The most obvious (and likely?) one is changing the ECU setting for how much it "blips" the engine when shifting gears or if/by how much it feeds a tiny bit of gas to the engine when you're off throttle as to keep the wheel speed and engine RPM closer. The engine braking effect can be very strong if not "dampened" like this and prove itself damaging to the powertrain as a whole with the stress it can put on the drivetrain. Drivers are probably more concerned with the former, but sometimes you can spot a race engineer asking the driver to change the EB or the "handbrake" setting for performance reasons.
The second guess is changing the MGU-K harvesting rate. Both the MGU-K and the engine slow down the driven axle by sapping its power, but the ERS has a harvest cap for the MGU-K and I guess the transition can be quite jarring when the limit is reached. The dial could change the balance for those two forces... But this is too deep into speculation territory for my liking.
Anyway Greco confirmed already that the engine braking value is validated by real data. The automatic throttle operation by the ECU could still happen but I think the devs have other challenges to work out yet before engaging with this one. We still have to see the BB being nailed down.
I would love that though! As well as brake migration.