Do wall cabinets have to be mounted directly on the wall?

Hello. We are currently having the kitchen planned by a kitchen studio. On one wall, there should first be a tall cabinet with an integrated dishwasher (59.8 cm deep), then a deep freestanding refrigerator (81 cm deep including rear spacer), and then another tall cabinet with an integrated oven (59.8 cm deep). The kitchen planner said this would not be a problem. The tall cabinets could be pulled 21.2 cm forward, and then the deep refrigerator would be flush with the tall cabinets on the left and right. Somehow, that seems strange to me. What do you think of the idea?

That is the eternal problem of SbS that stand within a tall kitchen cabinet wall. Pulling out the neighboring cabinets completely is not possible, however, you have to check what angle and space the doors of the SbS need.

Maybe reconsider the kitchen planning and get rid of the SbS ;).

SBS is a heartfelt wish of my wife... You might know this. If it were possible to bring forward the tall cabinets, we would do it. Does anyone else have an opinion on this?

SBS is a heart’s desire of my wife... You might know that. If it were possible to move the tall cabinets forward, we would do that as well. Does anyone have an opinion on this?

Of course, you can move them forward.
However, the side would have to be covered, as well as the tall cabinets secured at the top.
That should not be a problem.
Still: anyone who wants an SBS has not informed themselves properly and just blindly wants what is currently mainstream. Therefore, one should get informed about SBS first and not immediately shout “I want, I want, I want.” Then you can still look into alternatives or ways of “inclusion.”

SBS is a heartfelt wish of my wife... You might know that. If pulling out the tall cabinets were feasible, we would do it too. Does anyone else have an opinion on this?

Of course you can pull them out. However, then the side would need to be clad, as well as the tall cabinets fixed at the top. Should be no problem. Nevertheless: anyone who wants an SBS hasn’t properly informed themselves and just blindly wants what’s currently mainstream. So inform yourself about SBS first and don’t just shout "I want I want I want". Then you can still look into alternatives or ways of "inclusion".

... then a freestanding refrigerator ... and then still

"Freestanding" means freestanding because it is freestanding. If you install freestanding, it is called a built-in refrigerator, which is then not freestanding but built-in compatible.

Would it be an option to integrate your planned construction by boxing it in with a flush surrounding wall, which brings the rear wall about 80cm into the kitchen?