My laptop screen is black, but my secondary monitor is working (Ubuntu 20.04.5. LTS)

I've been using my laptop (Acer Nitro 5, AMD Ryzen) with an additional screen (connected via HDMI), daily, for about two months now, and it's been working fine. Now, the built-in display doesn't work at all (not even when booting), and only the secondary monitor does (on which I can't see the login screen). In the display settings, I can see that the built-in display only has the 640x480 resolution available as well.

Relevant inxi output:

System:
  Kernel: 5.4.0-137-generic x86_64 bits: 64 compiler: gcc 
  v: 9.4.0 Desktop: Gnome 3.36.9 info: plank wm: gnome-shell dm: GDM3 3.36.3 
  Distro: Ubuntu 20.04.5 LTS (Focal Fossa) 
Machine:
  Type: Laptop System: Acer product: Nitro AN515-43 v: V1.05 
  Mobo: PK model: Octavia_PKS v: V1.05  
  UEFI: Insyde v: 1.05 date: 08/07/2019 
CPU:
  Topology: Quad Core model: AMD Ryzen 5 3550H with Radeon Vega Mobile Gfx 
  bits: 64 type: MT MCP arch: Zen+ rev: 1 L2 cache: 2048 KiB 
  flags: avx avx2 lm nx pae sse sse2 sse3 sse4_1 sse4_2 sse4a ssse3 svm 
  bogomips: 33537 
  Speed: 1224 MHz min/max: 1400/2100 MHz boost: enabled Core speeds (MHz): 
  1: 1230 2: 1223 3: 1296 4: 1228 5: 1225 6: 1227 7: 1278 8: 1395 
Graphics:
  Device-1: AMD Baffin [Radeon RX 460/560D / Pro 
  450/455/460/555/555X/560/560X] 
  vendor: Acer Incorporated ALI driver: amdgpu v: kernel bus ID: 01:00.0 
  chip ID: 1002:67ef 
  Device-2: AMD Picasso vendor: Acer Incorporated ALI driver: amdgpu 
  v: kernel bus ID: 05:00.0 chip ID: 1002:15d8 
  Display: x11 server: X.Org 1.20.13 driver: amdgpu compositor: gnome-shell 
  resolution: 1920x1080~60Hz, 640x480~60Hz 
  OpenGL: renderer: AMD Radeon Vega 8 Graphics (RAVEN DRM 3.35.0 
  5.4.0-137-generic LLVM 12.0.0) 
  v: 4.6 Mesa 21.2.6 direct render: Yes 

Relevant xrandr output:

Screen 0: minimum 320 x 200, current 1920 x 1080, maximum 16384 x 16384
HDMI-A-0 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 476mm x 268mm
   1920x1080     60.00*+  50.00    59.94  
   1680x1050     59.88  
   1280x1024     75.02    60.02  
   1440x900      59.90  
   1280x960      60.00  
   1280x800      60.00  
   1280x720      60.00    50.00    59.94  
   1024x768      75.03    70.07    60.00  
   832x624       74.55  
   800x600       72.19    75.00    60.32    56.25  
   720x576       50.00  
   720x480       60.00    59.94  
   640x480       75.00    72.81    66.67    60.00    59.94  
   720x400       70.08  
eDP connected 640x480+0+0 (normal left inverted right x axis y axis) 0mm x 0mm
   640x480       59.94*