Writing in continuation to this discussion because I have thought that this is seems to be same problem I am having but no solution was provided here in the end.
I then enter the /src directory of LAMMPS to make the USER-PLUMED program with: "make yes-USER-PLUMED". The installation is successful and I end up with the files
cmake -C ../cmake/presets/std_nolib.cmake -D PKG_GPU=on -DBUILD_DOC=ON -DBUILD_OMP=ON -DCMAKE_C_COMPILER=/usr/bin/gcc-7 -DGPU_ARCH=sm_60 -DGPU_API=cuda -DBUILD_MPI=OFF -DCMAKE_CXX_COMPILER=/usr/bin/g++-7 -DCMAKE_INSTALL_PREFIX=/local/home/dmlocal/programs/compiled/lammps -D BUILD_SHARED_LIBS=OFF ../cmake
The compilation runs successfully but when it's time to link the executable I end up with this: exactly what Anna experienced.
....
[100%] Building CXX object CMakeFiles/lmp.dir/local/home/dmlocal/programs/source/lammps/src/GPU/pair_born_coul_wolf_cs_gpu.cpp.o
[100%] Building CXX object CMakeFiles/lmp.dir/local/home/dmlocal/programs/source/lammps/src/GPU/pair_born_coul_long_cs_gpu.cpp.o
[100%] Building CXX object CMakeFiles/lmp.dir/local/home/dmlocal/programs/source/lammps/src/GPU/pair_coul_long_cs_gpu.cpp.o
[100%] Linking CXX executable lmp
CMakeFiles/lmp.dir/local/home/dmlocal/programs/source/lammps/src/fix_plumed.cpp.o: In function `LAMMPS_NS::FixPlumed::post_force(int)':
fix_plumed.cpp:(.text+0x26a): undefined reference to `plumed_cmd'
fix_plumed.cpp:(.text+0x292): undefined reference to `plumed_cmd'
fix_plumed.cpp:(.text+0x2ae): undefined reference to `plumed_cmd'
fix_plumed.cpp:(.text+0x2d6): undefined reference to `plumed_cmd'
fix_plumed.cpp:(.text+0x2f4): undefined reference to `plumed_cmd'
CMakeFiles/lmp.dir/local/home/dmlocal/programs/source/lammps/src/fix_plumed.cpp.o:fix_plumed.cpp:(.text+0x323): more undefined references to `plumed_cmd' follow
CMakeFiles/lmp.dir/local/home/dmlocal/programs/source/lammps/src/fix_plumed.cpp.o: In function `LAMMPS_NS::FixPlumed::~FixPlumed()':
fix_plumed.cpp:(.text+0xc95): undefined reference to `plumed_finalize'
CMakeFiles/lmp.dir/local/home/dmlocal/programs/source/lammps/src/fix_plumed.cpp.o: In function `LAMMPS_NS::FixPlumed::~FixPlumed()':
fix_plumed.cpp:(.text+0xe75): undefined reference to `plumed_finalize'
CMakeFiles/lmp.dir/local/home/dmlocal/programs/source/lammps/src/fix_plumed.cpp.o: In function `LAMMPS_NS::FixPlumed::FixPlumed(LAMMPS_NS::LAMMPS*, int, char**)':
fix_plumed.cpp:(.text+0xf40): undefined reference to `plumed_create'
fix_plumed.cpp:(.text+0xf7a): undefined reference to `plumed_cmd'
fix_plumed.cpp:(.text+0x1001): undefined reference to `plumed_cmd'
fix_plumed.cpp:(.text+0x101d): undefined reference to `plumed_cmd'
fix_plumed.cpp:(.text+0x1039): undefined reference to `plumed_cmd'
fix_plumed.cpp:(.text+0x113c): undefined reference to `plumed_cmd'
CMakeFiles/lmp.dir/local/home/dmlocal/programs/source/lammps/src/fix_plumed.cpp.o:fix_plumed.cpp:(.text+0x116a): more undefined references to `plumed_cmd' follow
CMakeFiles/lmp.dir/local/home/dmlocal/programs/source/lammps/src/fix_plumed.cpp.o: In function `PLMD::Plumed::~Plumed()':
fix_plumed.cpp:(.text._ZN4PLMD6PlumedD2Ev[_ZN4PLMD6PlumedD5Ev]+0x1d): undefined reference to `plumed_finalize'
CMakeFiles/lmp.dir/local/home/dmlocal/programs/source/lammps/src/fix_plumed.cpp.o: In function `PLMD::Plumed::~Plumed()':
fix_plumed.cpp:(.text._ZN4PLMD6PlumedD0Ev[_ZN4PLMD6PlumedD5Ev]+0x2d): undefined reference to `plumed_finalize'