Mathematica ( and nearly all other programs) never use the graphics card if the CPU has a GPU unit. If there is no GPU in the CPU, only the standard VGA part plus memory is used.
In order to use capabilities of separate graphics cards, in Mathematica, you have to use the CUDA or OpenGL links and write your own procedures.
All these expensive computers with graphics cards are the same marketing stuff we know now for 27 years: Before anybody is coming to the point of using the extra hardware it is outdated.
Only if you have plans to work with expensive graphics software using the graphics card, mainly games, buy a RTX. Otherwise a cheap 730 or 1600 series will do.
