Sometimes the front shakes when driving uphill. The engine mount has been replaced, the gearbox mount has been replaced, the wheels have been balanced, the tires are healthy, the chassis has been checked. Maybe someone has encountered this and knows where else the problem could be? Car W218 CLS, rear-wheel drive.

are you at full rpm or just barely giving it gas?
Is engine loaded hard or just old lady driving?
Does speed matter?
What gear is it in and what is speed?

My guess is engine rpm too low and tranny is not downshifting, so engine is chugging as it does not have power to climb hill

last time it was when I was driving on 50km/h and 5th gear.
So it was not hard driving. Just I was driving in the city and there were small hillside.
Before this it was then i was driving on 80km/h and 7th gear.
Gears are automatic.
I would say it was "old lady driving"
It lasts just for few second till hillside ends.

I would lean on it more to force it to vibe so you can get a better feel for it. Eg; the center bearing support on the driveshaft can feel fine until you lean on it, and rpms make it worse. Guibo joints can do similar. You can also use a phone app to check the vibration frequency to narrow it down what part it is.

next time watch the engine speed and report back RPM.

I find sometimes the car tries too long to stay in high gears for whatever reason and has no power so any hill and the engine has to chug a bit and pray for a down shift so it will maintain speed.

To test manually downshift next time and if it goes away theirs your problem.

and maybe a tranny releanr procedure would help and every once in while drive it like you stole so the car knows how to behave

Yup, car likes to stretch its legs once a while : ) hence Italian tune-up : )