Now I've also had success installing the new nvidia driver (450).
After the failed install, I tried 'sudo apt -f install'. This also failed with error messages, pointing to /usr/lib/x86_64-linux-gnu/libGL.so.1.distrib and x86_64-linux-gnu/libGL.so.1.distrib, respectively, being modified by nvidia-340.
Well, nvidia-340 wasn't installed. I installed it and removed it again straight away. After that, it was possible to successfully install the nvidia-driver-450 through the additional drivers tool.
Now I've also had success installing the new nvidia driver (450).
After the failed install, I tried 'sudo apt -f install'. This also failed with error messages, pointing to /usr/lib/ x86_64- linux-gnu/ libGL.so. 1.distrib and x86_64- linux-gnu/ libGL.so. 1.distrib, respectively, being modified by nvidia-340.
Well, nvidia-340 wasn't installed. I installed it and removed it again straight away. After that, it was possible to successfully install the nvidia-driver-450 through the additional drivers tool.