the most common solution for this is using a program called wine(which helps you run programs made for windows on mac) to open windows UTAU and use different resamplers. though personally, it didn't work very well on my old computer. for some people it works though. i think my computer was just too old.
there's also this new program that's being made called UTSU, one of the goals of UTSU is to make it so that you can run any resampler on any computer with utsu on it. It currently hasn't implemented that if memory serves, since the program is still in development but i find that the default resampler for UTSU sounds less metallic than UTAU synth. ( heres the thread for utsu
https://utaforum.net/threads/utsu-a-cross-platform-vocal-synth-frontend.17476/page-11#post-146633 )
you can also try messing around with it in mixing. sometimes i try to cover it up a bit by raising bass a little bit... or i embrace the metallic-ness and go for a reverb-y auto-tuney effect instead. also, i think turning up the BRE helps slightly if you don't mind a raspier voice.