At 210k km the DPF is probably saturated with ash that cant be burned off through normal regen. You need a professional DPF cleaning - they remove it and clean it with a special machine. Costs around 300-500 EUR and its like having a new DPF.
Also check your glow plugs and EGR valve. If those arent working properly the regen cycle cant reach the right temperatures.
before spending money on cleaning, check the differential pressure sensor. its a small sensor on the DPF that measures how clogged it is. if the sensor is faulty it can report false readings and prevent regen from starting.
its a 50 EUR part and takes 10 minutes to replace. worth checking first.
Also make sure your oil is the correct spec. BMW LL-04 is required for diesel with DPF. Using the wrong oil will clog the DPF faster because of higher ash content.
We see this a lot - people use cheaper oil and wonder why their DPF keeps clogging.
