Will Voukoder be ready for Vegas Pro 18?

In the Vegas render dialog, you clicked on Voukoder. Then in Voukoder you selected custom template show voukoder dialog, and then codec h.264. DO you see a preset there for NVIDIA NVENC? If so, click on it and hit apply. You can then change options if you want to further tweak the settings.

The other main option is h.264 x264 which is higher quality but CPU driven.

kanilingus , see Chris's screenshot. Right above x.264 is H.264 NVIDIA NVENC, so highlight that and hit "apply."

If it still doesn't work, see Vouk's post about updating your NVIDIA drivers to the latest studio version (which you need to do anyway in Vegas- they make it easy- go to the help menu and select driver update in Vegas.)