no build possible on RPi4

[mk-fs]

The build stops with an error:

error: ‘cvWaitKey’ was not declared in this scope

I installed opencv (libopencv-dev) and BCM2838 Library (V1.71).

Same behaviour at a second new upset RPi4.
I need help with this issue.

here the outprint from terminal:

[ 84%] Linking CXX executable ../../../install/bin/PlayerThread
[ 84%] Built target PlayerThread
Scanning dependencies of target LePiServer
[ 88%] Building CXX object app/LePiServer/CMakeFiles/LePiServer.dir/LePiServer.cpp.o
[ 92%] Linking CXX executable ../../../install/bin/LePiServer
[ 92%] Built target LePiServer
Scanning dependencies of target LePiClient
[ 96%] Building CXX object app/LePiClient/CMakeFiles/LePiClient.dir/LePiClient.cpp.o
.../LePi/app/LePiClient/LePiClient.cpp: In function ‘int main()’:
.../LePi/app/LePiClient/LePiClient.cpp:119:19: error: ‘cvWaitKey’ was not declared in this scope
119 | int key = cvWaitKey(5);
| ^~~~~~~~~
make[2]: *** [app/LePiClient/CMakeFiles/LePiClient.dir/build.make:63: app/LePiClient/CMakeFiles/LePiClient.dir/LePiClient.cpp.o] Fehler 1
make[1]: *** [CMakeFiles/Makefile2:424: app/LePiClient/CMakeFiles/LePiClient.dir/all] Fehler 2
make: *** [Makefile:84: all] Fehler 2

[mk-fs]

in LePiServer.cpp at line 119, "cvWaitKey()" must be replaced by "cv::waitKey()"