Keyboard and Trackpad no function

Dear all,

after an issue with coffee over the keyboard / sticky keys i decided to replace the keyboard instead of the whole upper case. All keys where working (but sticky) at this time.

Replacement of keyboard done - but then no reaction on the keyboard / trackpad. Also no backlighting available. The only functioning key is the power button.

After this i replaced the 2 flex cables for the keyboard and the trackpad, again no help.

Tried several resets with charging cable in or out / NVRAM Reset / battery plugged off and on and so on, all no help.

With external keyboard over BT and mouse via USB Cable i could use the MacBook, but its annoying.

After this I had no further ideas, so i brought it to a repair shop. They told me, the cheapest repair is maybe a new upper case, in a very bad case they have to change the logic board, but then the repair costs are the same as a new actual MacBook Air.

As the power button works with the new keyboard, I assume that there is a chance to restore the normal functions.

Any ideas of an additional reset or what i can do?

Anybody here, who had the same trouble in the past?