External monitor not working anymore

I have been using Manjaro on my Thinkpad T420 since two years ago with no hardware problems. Most of the time I have the laptop connected to an external Samsung monitor via DisplayPort-to-HDMI adaptor and, recently, via VGA. The reason I switched from DP/HDMI to VGA was because the monitor stopped working after an update of the OS when connected via DP/HDMI. Since it was working via the VGA port, I just kept working and ignored the issue… Until yesterday, when I did another update of Manjaro and the external screen, although is detected by the system, is not working anymore.
My first thought was that there was a hardware problem. I tried the screen with another laptop, and it works with both the HDMI and VGA ports; as for the laptop, I am not sure, because I don’t have another external monitor to test it with.
Searching here in the Forum, I found a post suggesting to try older kernels, since this is old hardware (my laptop is from 2011). I rebooted the computer using kernels 4.14, 4.19, and 5.4, all of which I have happily used before, but without avail: the external monitor is detected (but is not working) when I use the VGA port, and is not detected at all if the DP/HDMI port is used instead (I reconnected the cables several times).
This might be a hardware failure, but any hint on how to be sure of the cause of the problem and find a solution?
Here are some outputs that might be helpful.

❯ inxi -Fazy
  Kernel: 4.19.180-1-MANJARO x86_64 bits: 64 compiler: gcc v: 10.2.0 
  parameters: BOOT_IMAGE=/boot/vmlinuz-4.19-x86_64 
  root=UUID=7237cc4d-9ab7-410c-90c4-b8c90e2b10df rw quiet apparmor=1 
  security=apparmor udev.log_priority=3 
  Desktop: KDE Plasma 5.21.3 tk: Qt 5.15.2 info: latte-dock wm: kwin_x11 vt: 1 
  dm: SDDM Distro: Manjaro Linux base: Arch Linux 
  Type: Laptop System: LENOVO product: 4180Q3U v: ThinkPad T420 
  serial: <filter> Chassis: type: 10 serial: <filter> 
  Mobo: LENOVO model: 4180Q3U serial: <filter> UEFI-[Legacy]: LENOVO 
  v: 83ET82WW (1.52 ) date: 06/04/2018 
  ID-1: BAT0 charge: 37.7 Wh (100.0%) condition: 37.7/56.2 Wh (67.1%) 
  volts: 12.4 min: 10.8 model: SANYO 45N1001 type: Li-ion serial: <filter> 
  status: Full 
  Info: Dual Core model: Intel Core i7-2640M bits: 64 type: MT MCP 
  arch: Sandy Bridge family: 6 model-id: 2A (42) stepping: 7 microcode: 2F 
  cache: L2: 4 MiB 
  flags: avx lm nx pae sse sse2 sse3 sse4_1 sse4_2 ssse3 vmx bogomips: 22326 
  Speed: 797 MHz min/max: 800/3500 MHz Core speeds (MHz): 1: 797 2: 797 3: 797 
  4: 797 
  Vulnerabilities: Type: itlb_multihit status: KVM: Vulnerable 
  Type: l1tf mitigation: PTE Inversion 
  Type: mds mitigation: Clear CPU buffers; SMT vulnerable 
  Type: meltdown mitigation: PTI 
  Type: spec_store_bypass 
  mitigation: Speculative Store Bypass disabled via prctl and seccomp 
  Type: spectre_v1 
  mitigation: usercopy/swapgs barriers and __user pointer sanitization 
  Type: spectre_v2 mitigation: Full generic retpoline, IBPB: conditional, 
  IBRS_FW, STIBP: conditional, RSB filling 
  Type: srbds status: Not affected 
  Type: tsx_async_abort status: Not affected 
  Device-1: Intel 2nd Generation Core Processor Family Integrated Graphics 
  vendor: Lenovo ThinkPad T420 driver: i915 v: kernel bus-ID: 00:02.0 
  chip-ID: 8086:0126 class-ID: 0300 
  Device-2: Chicony integrated camera type: USB driver: uvcvideo 
  bus-ID: 1-1.6:5 chip-ID: 04f2:b221 class-ID: 0e02 
  Display: x11 server: X.Org 1.20.10 compositor: kwin_x11 driver: 
  loaded: intel unloaded: modesetting alternate: fbdev,vesa display-ID: :0 
  screens: 1 
  Screen-1: 0 s-res: 1920x1980 s-dpi: 96 s-size: 507x523mm (20.0x20.6") 
  s-diag: 728mm (28.7") 
  Monitor-1: LVDS1 res: 1600x900 hz: 60 dpi: 131 size: 310x170mm (12.2x6.7") 
  diag: 354mm (13.9") 
  Monitor-2: VGA1 res: 1920x1080 hz: 60 dpi: 96 size: 510x290mm (20.1x11.4") 
  diag: 587mm (23.1") 
  OpenGL: renderer: Mesa DRI Intel HD Graphics 3000 (SNB GT2) 
  v: 3.3 Mesa 20.3.4 compat-v: 3.0 direct render: Yes 
  Device-1: Intel 6 Series/C200 Series Family High Definition Audio 
  vendor: Lenovo driver: snd_hda_intel v: kernel bus-ID: 00:1b.0 
  chip-ID: 8086:1c20 class-ID: 0403 
  Sound Server-1: ALSA v: k4.19.180-1-MANJARO running: yes 
  Sound Server-2: JACK v: 0.125.0 running: no 
  Sound Server-3: PulseAudio v: 14.2 running: yes 
  Sound Server-4: PipeWire v: 0.3.23 running: no 
  Device-1: Intel 82579LM Gigabit Network vendor: Lenovo ThinkPad T520 
  driver: e1000e v: 3.2.6-k port: 5080 bus-ID: 00:19.0 chip-ID: 8086:1502 
  class-ID: 0200 
  IF: enp0s25 state: up speed: 1000 Mbps duplex: full mac: <filter> 
  Device-2: Intel Centrino Advanced-N 6205 [Taylor Peak] driver: iwlwifi 
  v: kernel port: efa0 bus-ID: 03:00.0 chip-ID: 8086:0085 class-ID: 0280 
  IF: wlp3s0 state: up mac: <filter> 
  IF-ID-1: wwp0s29u1u4i6 state: down mac: <filter> 
  Device-1: Broadcom BCM2045B (BDC-2.1) type: USB driver: btusb v: 0.8 
  bus-ID: 1-1.4:4 chip-ID: 0a5c:217f class-ID: fe01 serial: <filter> 
  Report: This feature requires one of these tools: hciconfig/bt-adapter 
  Local Storage: total: 1.36 TiB used: 952.87 GiB (68.2%) 
  SMART Message: Unable to run smartctl. Root privileges required. 
  ID-1: /dev/sda maj-min: 8:0 vendor: Samsung model: SSD 860 EVO 500GB 
  size: 465.76 GiB block-size: physical: 512 B logical: 512 B speed: 6.0 Gb/s 
  rotation: SSD serial: <filter> rev: 3B6Q scheme: MBR 
  ID-2: /dev/sdb maj-min: 8:16 vendor: HGST (Hitachi) model: HTS541010A9E680 
  size: 931.51 GiB block-size: physical: 4096 B logical: 512 B speed: 6.0 Gb/s 
  rotation: 5400 rpm serial: <filter> rev: A7G0 scheme: MBR 
  ID-1: / raw-size: 65.37 GiB size: 63.84 GiB (97.67%) used: 47.02 GiB (73.7%) 
  fs: ext4 dev: /dev/sda1 maj-min: 8:1 
  ID-2: /home raw-size: 400.39 GiB size: 393.11 GiB (98.18%) 
  used: 216.01 GiB (54.9%) fs: ext4 dev: /dev/sda2 maj-min: 8:2 
  Alert: No Swap data was found. 
  System Temperatures: cpu: 49.0 C mobo: N/A 
  Fan Speeds (RPM): cpu: 3167 
  Processes: 205 Uptime: 19m wakeups: 1 Memory: 15.55 GiB 
  used: 3.06 GiB (19.7%) Init: systemd v: 247 tool: systemctl Compilers: 
  gcc: 10.2.0 clang: 11.1.0 Packages: 2061 pacman: 2054 lib: 461 flatpak: 0 
  snap: 7 Shell: Zsh v: 5.8 running-in: konsole inxi: 3.3.03

❯ xrandr --listproviders
Providers: number : 1
Provider 0: id: 0x4b cap: 0xb, Source Output, Sink Output, Sink Offload crtcs: 3 o
utputs: 9 associated providers: 0 name:Intel

❯ xrandr
Screen 0: minimum 8 x 8, current 1920 x 1980, maximum 32767 x 32767
LVDS1 connected primary 1600x900+170+1080 (normal left inverted right x axis y axis) 310mm x 170mm
   1600x900      60.00*+
   1400x900      59.88  
   1368x768      60.00    59.88    59.85  
   1280x800      59.81    59.91  
   1280x720      59.86    60.00    59.74  
   1024x768      60.00  
   1024x576      60.00    59.90    59.82  
   960x540       60.00    59.63    59.82  
   800x600       60.32    56.25  
   864x486       60.00    59.92    59.57  
   800x450       60.00  
   640x480       59.94  
   720x405       59.51    60.00    58.99  
   640x360       59.84    59.32    60.00  
DP1 disconnected (normal left inverted right x axis y axis)
DP2 disconnected (normal left inverted right x axis y axis)
DP3 disconnected (normal left inverted right x axis y axis)
HDMI1 disconnected (normal left inverted right x axis y axis)
HDMI2 disconnected (normal left inverted right x axis y axis)
HDMI3 disconnected (normal left inverted right x axis y axis)
VGA1 connected 1920x1080+0+0 (normal left inverted right x axis y axis) 510mm x 290mm
   1920x1080     60.00*+
   1600x1200     60.00  
   1680x1050     59.95  
   1280x1024     60.02  
   1440x900      59.89  
   1280x960      60.00  
   1280x800      59.81  
   1024x768      60.00  
   800x600       60.32    56.25  
   640x480       59.94  
VIRTUAL1 disconnected (normal left inverted right x axis y axis)

OK, I managed to test my laptop with Ubuntu and Windows 10, and in both cases the symptoms are as described before. Therefore, this is a hardware problem, not related to Manjaro. Apologies for the noise.

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