OS: Manjaro 18.0.2 Illyria
Kernel: x86_64 Linux 4.20.0-1-MANJARO
Resolution: 4480x1440 (#1: 2560x1440 | #2: 1920x1080p)
DE:      Xfce4
WM:   Xfwm4 (compositor: OFF)

CPU:  AMD Ryzen 7 2700X Eight-Core @ 16x 3.7GHz-4.2GHz
GPU:  Radeon RX 570 Series (POLARIS10, DRM 3.27.0, 4.20.0-1-MANJARO, LLVM 8.0.0, Mesa.19.0.0_devel.106524 )
RAM: 16GB

Reportedly ran in Vulkan(SM5) mode.  Flickers to black quite heavily, did 2 runs, first run was stuttery, 2nd was smoother, both exhibited flicker. the first run was flicker at the start, then none, 2nd run was constant flicker for the entire run.

Other than that, performance metrics were in line with what I'd expect from a stock RX 570 running @1440p.

EDIT: To clarify, this was performance test 2.1.0. And I submitted my results on run #2.

Just wanted to link to this comment section: https://www.gamingonlinux.com/articles/an-enhanced-version-of-the-fan-made-half-...
As it illustrates this is a pervasive issue with all AMD hardware regardless of Proprietary or Open-Source drivers.

Especially pay attention to the post by YoRHa-2B (The lead-developer of DXVK, Someone unarguably extremely intimate with both D3D11 and Vulkan):
[excerpt]

"running it with validation layers enabled indicates that there are quite a few bugs in the Vulkan render path. Including invalid shaders, invalid image layout transitions, out-of-bounds image copies, all the fun stuff that leads to undefined behaviour. How does this even work on Nvidia?"

So it's not a problem on Project Borealis' side, but an issue on Epics' side. One of Vulkan's primary goals as an API is to provide such strict driver and specification validation that this sort of thing is avoided completely. But as has been a multi-decade trend Nvidia are arbitrarily "defining" undefined-behaviour driver side instead of forcing the developer to fix their broken code client/backend side. This is honestly quite egregious :(

https://www.youtube.com/playlist?list=PLVEKGwbIcqgedS3QUHGAxXFs5976HmoCJ <--- all test runs recorded

https://gitlab.com/snippets/1796775 <---- log files of each test run

it seems flickering a lot on amdgpu