@ubname: installing the meta-package worked here, but you can install the single packages manually:
sudo apt install libnvidia-gl-390/bionic-proposed libnvidia-compute-390/bionic-proposed libnvidia-decode-390/bionic-proposed libnvidia-encode-390/bionic-proposed libnvidia-ifr1-390/bionic-proposed libnvidia-fbc1-390/bionic-proposed
You might have to do the same for the i386 dependencies.
@ubname: installing the meta-package worked here, but you can install the single packages manually:
sudo apt install libnvidia- gl-390/ bionic- proposed libnvidia- compute- 390/bionic- proposed libnvidia- decode- 390/bionic- proposed libnvidia- encode- 390/bionic- proposed libnvidia- ifr1-390/ bionic- proposed libnvidia- fbc1-390/ bionic- proposed
You might have to do the same for the i386 dependencies.