Movie Edit Pro is quite capable of not using a GPU and using purely the CPU but the results may not be that good for playback resulting in jagged looking video while editing. That can be improved by reducing the quality of the video feed in MEP and reducing frame rates which will result in a softer looking preview but will not effect the export quality. To get smoother playback and faster export times using hardware encoding rather than software encoding then the use of a GPU can improve things. First I think people here will say that using an Intel processor with an inbuilt graphics chip capable of using Intel's Graphics 520 and above (the higher the better) would be the first and most cost effective way to use MEP. Then possibly an NVIDIA card would help but again I would recommend at 1060 card or above with 6gig of onboard memory although lower cards can perform but possibly not that well for above HD export. Then a combination of Intel internal chip with an NVIDIA card but the Intel chip set to background use. Matrox cards have been known to work but how effective and what type to recommend I don't personally know. All we know is such systems have been tested by Magix and known to run but how well compared to other systems I don't know.
There are a lot of other factors to take into account such as how much physical memory you have, type and speed of main CPU as well as hard drive speeds, types and sizes. How far to take a machine in it's specs before cost overtakes benefits is hard to say.
. . . . Someone told me that only Nvidia cards is available currently . . . .
Unfortunately for Movie Edit Pro (MEP) this is not correct, for its big brother Video Pro X (VPX) this is only partially correct - see below.
Is this for an existing computer or new?
For maximum performance the computer/laptop requires an Intel processor with integrated GPU - as a minimum the iGPU recommended is the Intel Graphics HD 520 if you are working with Full HD (1920x1080) and/or HEVC video. For 4K video an Intel processor with a UHD 620 or better is preferred.
Without the iGPU as @CubeAce has stated performance will be poor as you are relying entirely on the processor to do all the rendering.
For both MEP and VPX product specifications, for maximum performance, an Intel iGPU is required.
Movie Edit Pro's big brother Video Pro X can use a NVidia graphics card, 1050 or better, however only for HEVC export and it still needs an Intel integrated GPU for maximum performance.