Ideally, cleaning and protecting this area are to be done after every wash rather than a standalone job. There are two ways to clean this area. Rinseless or waterless.
The first method of cleaning this area is to use Optimum No Rinse Wash (ONR or ONRW but I prefer the latter for added protection).
Dilute the cleaner accordingly in a bucket and use a microfiber towel. Much like wiping our furniture, the idea is to get the microfiber towel damped but not dripping wet. Rinse the towel when it picked up too much dirt. Always wipe from top to bottom.
Start by cleaning the door jambs and move on to the door panels side and lower edges.
Be sure to clean in between the rubber seals. Pinch the seals in between the towel and wipe. Those are some pretty dirty areas that could get neglected.
Another simpler cleaning method is to use a waterless wash (see more details here).
"Prime" the towel with the waterless wash product until it is damped. Wipe in similar fashion as above. Rinse or change to another microfiber towel when it is soiled.
These two methods can also be used to clean car boot jambs and fuel cap cover areas. In fact, they can be used to clean all interface areas and weather seals.
Once cleaned and dried, I would follow with some dressings on the rubber seals. You can read more about dressings under the interior care post here. The idea is to protect the rubber seals from premature drying, cracking, and shrinking. These failures would lead to less sound-proofing and in worst case water leakage.
I would apply some dressings on a microfiber towel and use the towel to wipe on the seals.
Similar to cleaning, dressings could be applied to all rubber seals and plastic surfaces.
This sums it all for the "twilight zone". It is not too hard to get this done after every wash.