Build inside differently than approved?!

If you only wanted to collect the subsidy, you plan the "bathroom" as a separate guest WC from the start. And the kitchen is just a normal room with the appropriate connections, which can be easily concealed.

You have no idea how creative people get when it comes to cheating...

Yes, yes, I believe that immediately. :-) You never know how the subsidy will proceed anyway, and such "granny flats" are already under scrutiny.

I'll skip all the moralizing because that wasn't the question. It won't be noticed if no neighbor reports it. But if someone is annoyed by the cars and asks whether having a granny flat there at [xy] is normal, then....
So, make something out of it.

We are planning to build with a granny flat on the ground floor

Counterproposal: don’t waste any thoughts on parking spot tricks, but rather browse around here a bit: clear the forest of numerous threads with the keywords "Einlieger" or "Einliegerwohnung" by first reading those with the keywords "Klumpenrisiko" and "Losgröße". Because trying to play landlord with just one single granny flat “paid off” only in fairy tales, back when instead of the 10e it was still the 7b responsible for it. This supposed extra income – often dreamed of as a turbo button for repayment – is actually more of a liquidity risk.

We are planning to build with a granny flat on the ground floor and therefore need three parking spaces.

Do you want to rent out the granny flat and if so, to how many people? I consider it quite possible that neighbors, as long as they follow the rule themselves, might complain about it. Fewer parking spaces means more cars are parked in public areas, which neighbors might object to for various reasons. Would you like to show your garden and outdoor layout plan? Maybe one of the ingenious forum members here will see a solution that you or your employees haven’t thought of.

We bought a plot of land in a new development area and are wondering what happens if we build differently inside than what was approved in the building notification.

...
In other words, we would only change one thing in the plan, namely a larger door between the two adjacent living rooms (in the main house and the granny flat).
However, we do not actually intend to build this door.

Will someone come and check this at some point? ?

And you think that the responsible office will not check this change against the building notification? Especially when there is funding involved, they will definitely wonder if someone is simply giving up a granny flat after the issue of parking spaces came up or just quickly has a door drawn in for it. Especially when the requirements are so detailed regarding positions and accessibility.
Building authorities do not like to be fooled and know the tricks of builders quite well. At least, that is my experience.

Thank you very much for all the answers. The granny flat exists for one reason: so that the family is part of the house, because my mother is supposed to move in. There is no economic interest in responding to your post 11ant. No parking spaces may be created behind the building line, i.e. in the garden. We actually have to build the house narrower, but then the granny flat won't work... we have applied for double KfW funding. Do I still have to specify the granny flat in the building notification?