Note, you must delete your cmakecache manually instead of only running the cmake command with the new KICAD_FINDPROTOBUF blah arg. The partial regeneration does not work with protobuf’s cached variables.
this is what it looks for me in the protobud section:
//Path to a file.
Protobuf_INCLUDE_DIR:PATH=/usr/include
//Path to a library.
Protobuf_LIBRARY_DEBUG:FILEPATH=/usr/lib/x86_64-linux-gnu/libprotobuf.a
//Path to a library.
Protobuf_LIBRARY_RELEASE:FILEPATH=/usr/lib/x86_64-linux-gnu/libprotobuf.a
//Path to a library.
Protobuf_LITE_LIBRARY_DEBUG:FILEPATH=/usr/lib/x86_64-linux-gnu/libprotobuf-lite.a
//Path to a library.
Protobuf_LITE_LIBRARY_RELEASE:FILEPATH=/usr/lib/x86_64-linux-gnu/libprotobuf-lite.a
//The Google Protocol Buffers Compiler
Protobuf_PROTOC_EXECUTABLE:FILEPATH=/usr/bin/protoc
//Path to a library.
Protobuf_PROTOC_LIBRARY_DEBUG:FILEPATH=Protobuf_PROTOC_LIBRARY_DEBUG-NOTFOUND
//Path to a library.
Protobuf_PROTOC_LIBRARY_RELEASE:FILEPATH=Protobuf_PROTOC_LIBRARY_RELEASE-NOTFOUND
I do yet it still fails with the protobuf