No second monitor

xfce4-display-settings don't show the second monitor connected via HDMI. Second screen remains dark, but is reacting so far, as alternative compupter displays vanished (hdmi-switch)

at Xubuntu-session, AMD Ryzen 5 4600U with Radeon Graphics 15803MB Notebook Ubuntu 20.04 LTS

$ inxi -Gxxx

Graphics: Device-1: AMD Renoir vendor: Lenovo driver: N/A bus ID: 03:00.0 chip ID: 1002:1636 Display: x11 server: X.Org 1.20.8 driver: ati,fbdev unloaded: modesetting,radeon,vesa resolution: 1920x1080~77Hz OpenGL: renderer: llvmpipe (LLVM 9.0.1 128 bits) v: 3.3 Mesa 20.0.4 compat-v: 3.1 direct render: Yes

$ uname -a

Linux MYNAME 5.4.0-37-generic #41 (closed)-Ubuntu SMP Wed Jun 3 18:57:02 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

$ lspci -v

[...]

03:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Renoir (rev ce) (prog-if 00 [VGA controller]) Subsystem: Lenovo Renoir Flags: bus master, fast devsel, latency 0, IRQ 11 Memory at d0000000 (64-bit, prefetchable) [size=256M]

$ hwinfo

[...]

20: PCI 300.0: 0300 VGA compatible controller (VGA) [Created at pci.386] Unique ID: svHJ.FeTiqCxFz54 Parent ID: JZZT.e+TNXSUNut3 SysFS ID: /devices/pci0000:00/0000:00:08.1/0000:03:00.0 SysFS BusID: 0000:03:00.0 Hardware Class: graphics card Model: "ATI Renoir" Vendor: pci 0x1002 "ATI Technologies Inc" Device: pci 0x1636 "Renoir" SubVendor: pci 0x17aa "Lenovo" SubDevice: pci 0x381b Revision: 0xce Memory Range: 0xd0000000-0xdfffffff (ro,non-prefetchable) Memory Range: 0xe0000000-0xe01fffff (ro,non-prefetchable) I/O Ports: 0x1000-0x10ff (rw) Memory Range: 0xfc400000-0xfc47ffff (rw,non-prefetchable) Memory Range: 0x000c0000-0x000dffff (rw,non-prefetchable,disabled) IRQ: 11 (no events) Module Alias: "pci:v00001002d00001636sv000017AAsd0000381Bbc03sc00i00" Driver Info #0: Driver Status: amdgpu is active Driver Activation Cmd: "modprobe amdgpu" Config Status: cfg=new, avail=yes, need=no, active=unknown Attached to: #35 (closed) (PCI bridge)