One good way of gauging what GPU you need is by looking at the Homeworld 3 system requirements. There we can see that the minimum requirements ask of a Nvidia GTX 1060, AMD R9 480, or the newer Intel Arc A380. Recommended specs instead suggest a GTX 1080 Ti, RX 5700 or Arc 580.
Though those Intel GPU suggestions are more modern given their relatively recent entry to the discrete graphics, the AMD and Nvidia options are a bit dated. Not that they aren't capable, but sourcing one of these older cards generally means looked for a used one, so we're going to bring you up to date with some much newer options which you can enjoy for years to come. Below we can present our hand-picked selection for a variety of budgets.