I’m thinking that it is already the second update of the 4.20 kernel on Thumbleweed and the nvidia drivers from suitable Repository are not there yet, I’m using the Kernel 4.19 and it’s no problem, someone will say … ask Nvidia!:P:sarcastic:
Hi
Ask Nvidia 
So, your correct, still at 4.19.x;
https://download.nvidia.com/opensuse/tumbleweed/x86_64/
Maybe having build issues…
Or switch to the ‘hard’ way?
https://en.opensuse.org/SDB:NVIDIA_the_hard_way
FWIW, I have successfully avoided Nvidia driver kerfluffles with Tumbleweed for many months now by following this system:
(1) Nvidia installed the hard way, as per malcomlewis’ link, without DKMS.
(2) When a new kernel looms on the horizon – from 4.19 to 4.20, say – I check Robert Gadsdon’s site:
for news on whether or not the new kernel works with Nvidia drivers available at: https://download.nvidia.com/XFree86/Linux-x86_64/ . If Mr. Gadsdon gives a “thumbs up,” I dup to the new kernel. If not, I wait.
I use the 4.19 kernel without hitting too much, I know I could use the hard way, but I do not see the reason
I wait patiently for the repository to update
As soon as the update of Nvidia from the Repository and the Kernel 4.20.2 has arrived, OK works;)
Yup this post is literally everything in a nutshell. 4.20.2 + nvidia 415.27 working great here.