Some interesting discussion here. I was going to keep quiet, maybe I still should...
I don't have a ton of VW experience. I do have some experience with BMW and temperature management with N55 engines and associated ECUs, and a lot of anecdotal things I've heard in BMW circles.
1/ In BMW circles with N54 and N55 engine variants with no oil coolers, some folks have tried to respond to high oil temps by increasing viscosity/HTHS. This made oil temps even higher (now you have drag on heavier oils to add to the mix). This could happen to this GTI. The only way to know is to try. Higher HTHS oil may increase engine protection but will do nothing for the temperatures.
2/ My particular N55 has an oil/coolant heat exchanger (oil/air is an option on "sport" and "high speed" variants). I didn't know what this GTI has but some posts here seem to have filled in that it is equipped similarly. As mentioned by someone, BMW has a number of cooling strategy targets depending on operating conditions. My tune (MHD) allows me to override and pick different cooling strategies depending on a few factors, primarily to bring temps down in more conditions by choice of the driver. I *assume* that VW has different cooling targets and, when driven aggressively, is the target coolant temp reduced? I know that there is talk of warranty so a tune is probably out of the question, but I am curious what programming VW has and if there are any options for the owner to reduce the targets. One mode offered by my tune is a "pre-cool" mode, where the target is set extra low (in the 80s C) to set while idling prior to beginning a "run". Something like that could be valuable to the owner. The different cooling targets are built into the factory ECU code, but selecting their use at different times is the function added by the tune.
3/ During or at the completion of a run, what are the coolant target, coolant temp and oil temp relative to one another? There's a screenshot in the thread which shows coolant at 100C and oil at 232F in the same shot. I'm not sure if this is the car in question. There are suggestions to lower the concentration of coolant and run the heat full blast. These will increase cooling system heat capacity and shed more heat (respectively), but...
a/ if 100C is the coolant target temp, then the system is keeping up with demand. Running the heat might not do a thing, though does technically shed more heat. If 100C is the target, the rest of the system will just work less hard to shed heat while the driver cooks.
b/ if the coolant is 100C while the oil is significantly hotter, then an issue is transferring heat from oil to coolant fast enough. Things that could help -- cooler coolant, more oil or coolant flow in the exchanger, larger heat exchanger. My oil/coolant heat exchanger is only about the size of my fist. I don't know that either altering the mixture or running the heat would affect the transfer of heat from oil to coolant.
A thermostatically controlled oil/air heat exchanger mounted where there is good airflow would be my vote on the "right" way to solve the problem, but I think others have already concluded this

I wonder if the owner can source genuine VW parts for other models (like the R) to retrofit the feature to their car while maximizing the chances of preserving warranty.