Dryer sheets
Found the "dry" dryer sheet kind (paper packaging, grainy sometimes semi-transluscent texture, waxy feel) does barely work.
However, the wet type of dryer sheet stored in a damp-wipe-style plastic package do work descently well.
But, with basicly any HP dryer, softner smell does remain.
And except for a fine dust cought by the filter, our Bauknecht back home still dryers perfectly fine after several years of heavy use.
Reversing on a HP dryer technicly only wastes time on most loads.
No airflow, no drying. Even small decreases make a huge difference.
Some heatpumps would have to turn off during reversing.
And then some heatpumps can't immediatly restart, adding several minutes to the cycle and often self-defeating the reversing as that wait time takes away from the time until next reverse.
Our Bauknecht back home does blocks of reversing with the heatpump off, on the other hand ours here reverses with heatpump on, but only briefly every 10min.
Thus, even Miele has now added a specific bedding cycle for more reversing and - in typical Miele fashion - instead of blindly reversing, reversing periods get more and more common as drying progresses.
On the open refill TwinDos cartridges, Miele has been expanding its non-machine sector agressivly for years now.
Thus, they blocked out the selection for other detergents.
But me being somewhat doubtfull of the system I would assume the electronics do have the same setup ay previous and changing the country setting would unlock that feature.
But, not sure on that though, I think you could get at least one cartridge to work with a refillable one.
The machine offers the option to adjust the dosage depending on water hardness in ml.
What I don't know if those are set values OR if it is the same setting system with up to 300ml selectable.
If they are freely selectable, you could just exchange the main detergent cartridge with refillable one and the whites one with water or your own liquid oxy additive. (AFAIK both are dispensed ALWAYS, just the ratios are changed for colors).