Confirmed SimpleDRM is active on my system:
[drm] Initialized simpledrm 1.0.0 for simple-framebuffer.0 on minor 0
simple-framebuffer simple-framebuffer.0: [drm] fb0: simpledrmdrmfb frame buffer 
device
This appears very early in boot, before the real GPU drivers (amdgpu/i915) 
initialize — matching the ArchWiki's description of Plymouth using SimpleDRM on 
the UEFI framebuffer specifically to avoid waiting on GPU driver load time.
Given this, my working theory is: boot is reliable because SimpleDRM guarantees 
an early framebuffer regardless of GPU driver state, but shutdown has no 
equivalent — Plymouth depends entirely on whichever real driver (amdgpu/i915) 
is still active, and if that driver is already unloading (which lines up with 
the fbcon: Taking over console message I found earlier), there's nothing left 
for plymouthd to draw onto.
Does Plymouth (or the kernel) have any path to fall back to SimpleDRM/EFI 
framebuffer during shutdown, the way it does at boot? If not, that asymmetry 
alone could fully explain missing shutdown splashes on systems where the real 
driver unloads before Plymouth's shutdown draw call happens.

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https://bugs.launchpad.net/bugs/2160567

Title:
  Plymouth splash does not appear on shutdown/reboot (works correctly on
  boot) — TPM-backed FDE, dual GPU (Intel + AMD)

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