Radeon HD 5770 driver/screen resolution pains

On a rusty bucket of bolts and new to Linux, what could possibly go wrong? Sorry if I’m missing something very obvious here. Latest version of Manjaro with KDE, mhwd only suggests and installs video-linux and while the performance is fairly snappy I can’t set my screen resolution above 1024x768, which makes for an unpleasant experience.

Graphics: Device-1: AMD Juniper XT [Radeon HD 5770] vendor: Micro-Star MSI driver: radeon
v: kernel bus ID: 01:00.0 chip ID: 1002:68b8
Display: x11 server: X .Org 1.20.10 compositor: kwin_x11 driver: ati,radeon
unloaded: modesetting alternate: fbdev,vesa display ID: :0 screens: 1
Screen-1: 0 s-res: 1024x768 s-dpi: 96 s-size: 270x203mm (10.6x8.0")
s-diag: 338mm (13.3")
Monitor-1: DVI-0 res: 1024x768 hz: 60
OpenGL: renderer: AMD JUNIPER (DRM 2.50.0 / 5.9.16-1-MANJARO LLVM 11.0.0)
v: 3.3 Mesa 20.3.1 compat-v: 3.1 direct render: Yes


              NAME               VERSION          FREEDRIVER           TYPE

       video-linux            2018.05.04                true            PCI
     network-r8168            2016.04.20                true            PCI

What’s the output of:

xrandr

Please use the Preformatted text </> button, not the Quote " button when pasting terminal output.