There is no Nvidia tag. Confer, https://superuser.com/questions/tagged/nvidia.
A separate, synonomized nvidia tag isn't really needed because as soon as the user starts typing nvidia in the tag area, [nvidia-graphics-card] automatically pops up (along with other nvidia options).
In the comments, you mentioned that the actual issue is trying to search on nvidia, which returns no matches. If we recreate the nvidia tag and synonomize it with nvidia-graphics-card, that creates a different problem. There are seven nvidia-related tags, and the resulting search on nvidia would exclude roughly a third of the nvidia questions. So the results would be misleading.
You can search on the word "nvidia" rather than the tag, but that isn't perfect, either. In the question, posters may refer to the "model name" of the card without mentioning "nvidia", so the search wouldn't capture everything.
There's actually a solution that isn't advertised, so people might not think to try it. You can use wildcards in tag name search terms. Searching on [nvidia*] returns everything with a tag name starting with "nvidia". It might be helpful for SE to include that information in the search help. I posted a suggestion to do that on Meta SE.