picasso*.bin files are part of firmware-amd-graphics package.
$ apt-file search picasso_asd.bin
firmware-amd-graphics: /lib/firmware/amdgpu/picasso_asd.bin
These files are present in your system when you package installed.
Their presence doesn't mean that they will get loaded.
I can see in your inxi:
$ inxi -G
Graphics: Device-1: Advanced Micro Devices [AMD/ATI] Picasso driver: N/A
Display: server: X.Org 1.20.11 driver: loaded: ati,vesa
unloaded: fbdev,modesetting,radeon resolution: 1440x876~1Hz
OpenGL: renderer: N/A v: N/A
You have no driver loaded, because you added nomodeset to boot
parameters. nomodeset instructs Linux kernel to not load video drivers.
You have installed non-free drivers (firmware-amd-graphics) and told
kernel not to load them.
Try without nomodeset and report back.
I may have missed your reply if you already did, please try to reply
with one post, not several consecutive posts, to keep discussion more
organized.
I can see that you said "It enables display twitching during boot. When
XDM gains control, it will try to set the display mode."
You have to continue tests without nomodeset option, otherwise you have
no driver and that's it.
