Astilex You should check this discussion: https://discuss.getsol.us/d/1899-radeon-rx-5700xt
TLDR: Currently Solus doesn't have the 5.3 kernel because it prevents NVidia users from booting. And when it will have it, there's no guarantee that it will work because you would need to successfully install it first from an ISO with an older kernel, and so far I haven't succeeded doing that.
I haven't tried Manjaro, but I'm running Fedora 31 (beta iso, final version to be released soon) and it works fine, until the day that I can run Solus again. 🙂