Tested with PureOS Byzantium KDE amd64 ISO from 2022-02-22.

Requires non-free firmware to be loaded from the host.

$ lspci -vvnnk
00:01.0 VGA compatible controller [0300]: Advanced Micro Devices, Inc. [AMD/ATI] Kaveri [Radeon R7 Graphics] [1002:1313] (prog-if 00 [VGA controller])
    Subsystem: ASRock Incorporation Kaveri [Radeon R7 Graphics] [1849:1313]
    Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
    Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
    Latency: 0, Cache Line Size: 64 bytes
    Interrupt: pin A routed to IRQ 10
    IOMMU group: 0
    Region 0: Memory at c0000000 (64-bit, prefetchable) [size=256M]
    Region 2: Memory at d0000000 (64-bit, prefetchable) [size=8M]
    Region 4: I/O ports at f000 [size=256]
    Region 5: Memory at ff700000 (32-bit, non-prefetchable) [size=256K]
    Expansion ROM at 000c0000 [disabled] [size=128K]
    Capabilities: <access denied>
    Kernel modules: radeon, amdgpu

$ sudo dmesg
[    2.775156] [drm:radeon_pci_probe [radeon]] *ERROR* radeon kernel modesetting for R600 or later requires firmware installed
[    2.775350] See https://wiki.debian.org/Firmware for information about missing firmware