Manjaro Linux is for Nvidia gpus. For Amd gpus, it has too old kernel and Mesa.
Use Debian sid Xfce with a latest custom kernel from kernel.org or
https://cgit.freedesktop.org/~agd5f/linux and the Oibaf ppa Mesa bionic
version.

xfce@ryzenpc:~$ inxi -bM
System:    Host: ryzenpc Kernel: 4.20.0-rc3+ x86_64 bits: 64 Desktop: Xfce
4.12.4 Distro: Debian GNU/Linux buster/sid 
Machine:   Type: Desktop Mobo: ASUSTeK model: PRIME B350M-K v: Rev X.0x serial:
<root required> UEFI: American Megatrends 
           v: 4023 date: 08/20/2018 
CPU:       6-Core: AMD Ryzen 5 1600 type: MT MCP speed: 2809 MHz 
Graphics:  Device-1: Advanced Micro Devices [AMD/ATI] Ellesmere [Radeon RX
470/480] driver: amdgpu v: kernel 
           Display: x11 server: X.Org 1.20.3 driver: amdgpu resolution:
3840x2160~60Hz 
           OpenGL: renderer: Radeon RX 570 Series (POLARIS10 DRM 3.27.0
4.20.0-rc3+ LLVM 7.0.1) 
           v: 4.5 Mesa 19.0.0-devel (git-bacf847 2018-12-04 bionic-oibaf-ppa)
Uptime: 11h 34m