Garbled video with artifacts and black zones on Dell Precision M90 - NVIDIA Corporation G71GLM [Quadro FX 2500M] (rev a1)

Experienced the faulty behaviour in the title with three different distros:

1. Manjaro 20.1 KDE
2. Ubuntu (ubuntu-20.10-desktop-amd64)
3. Gentoo (kernel 5.4.72-gentoo-x86_64)

With Manjaro and Ubuntu the system as it came out of the installation process was impossible to work with.

With Gentoo, the Plasma login page keeps flashing (alternating dark and light colours), once logged in into KDE, the desktop is reasonably stable, but artifacts begin to appear as soon as I start any program. Kde System settings application starts with a totally black or garbled menu on the left, which starts to appear when I click on it and move the pointer over.

Gentoo dmesg extract:

[ 1.274225] nouveau 0000:01:00.0: NVIDIA G71 (049a00a2)

[ 1.295280] battery: ACPI: Battery Slot [BAT0] (battery present)

[ 1.486179] nouveau 0000:01:00.0: bios: version 05.71.22.16.16

[ 1.486814] nouveau 0000:01:00.0: fb: 512 MiB GDDR3

[ 1.537506] [TTM] Zone kernel: Available graphics memory: 1015108 KiB

[ 1.537561] [TTM] Initializing pool allocator

[ 1.537617] [TTM] Initializing DMA pool allocator

[ 1.537678] nouveau 0000:01:00.0: DRM: VRAM: 505 MiB

[ 1.537728] nouveau 0000:01:00.0: DRM: GART: 512 MiB

[ 1.537780] nouveau 0000:01:00.0: DRM: TMDS table version 1.1

[ 1.537830] nouveau 0000:01:00.0: DRM: TMDS table script pointers not stubbed

[ 1.537882] nouveau 0000:01:00.0: DRM: DCB version 3.0

[ 1.537932] nouveau 0000:01:00.0: DRM: DCB outp 00: 03000323 00000004

[ 1.537984] nouveau 0000:01:00.0: DRM: DCB outp 01: 01011300 00000028

[ 1.538035] nouveau 0000:01:00.0: DRM: DCB outp 02: 020223f1 0040c080

[ 1.538085] nouveau 0000:01:00.0: DRM: DCB outp 03: 08035312 00000000

[ 1.538136] nouveau 0000:01:00.0: DRM: DCB outp 04: 04036312 00000000

[ 1.538186] nouveau 0000:01:00.0: DRM: DCB conn 00: 0041

[ 1.538236] nouveau 0000:01:00.0: DRM: DCB conn 01: 0100

[ 1.538286] nouveau 0000:01:00.0: DRM: DCB conn 02: 0310

[ 1.538335] nouveau 0000:01:00.0: DRM: DCB conn 03: 0311

[ 1.538384] nouveau 0000:01:00.0: DRM: DCB conn 04: 0313

[ 1.538434] nouveau 0000:01:00.0: DRM: DCB conn 05: 0254

[ 1.538483] nouveau 0000:01:00.0: DRM: DCB conn 06: 0455

[ 1.539110] nouveau 0000:01:00.0: DRM: MM: using M2MF for buffer copies

[ 1.539447] nouveau 0000:01:00.0: DRM: Saving VGA fonts

[ 1.592350] nouveau 0000:01:00.0: DRM: unknown connector type 54

[ 1.592416] nouveau 0000:01:00.0: DRM: unknown connector type 55

[ 1.593718] [drm] Supports vblank timestamp caching Rev 2 (21.10.2013).

[ 1.593768] [drm] Driver supports precise vblank timestamp query.

[ 1.595175] nouveau 0000:01:00.0: DRM: Calling LVDS script 6:

[ 1.595227] nouveau 0000:01:00.0: DRM: 0xC81B: Parsing digital output script table

[ 1.875313] nouveau 0000:01:00.0: DRM: Setting dpms mode 3 on TV encoder (output 2)

[ 2.001464] nouveau 0000:01:00.0: DRM: allocated 1920x1200 fb: 0x9000, bo (ptrval)

[ 2.015735] fbcon: nouveaudrmfb (fb0) is primary device

[ 2.148446] nouveau 0000:01:00.0: DRM: Calling LVDS script 2:

[ 2.148449] nouveau 0000:01:00.0: DRM: 0xC89F: Parsing digital output script table

[ 2.296610] nouveau 0000:01:00.0: DRM: Calling LVDS script 5:

[ 2.296613] nouveau 0000:01:00.0: DRM: 0xC80C: Parsing digital output script table

[ 2.423418] Console: switching to colour frame buffer device 240x75

[ 2.424634] nouveau 0000:01:00.0: fb0: nouveaudrmfb frame buffer device

[ 2.424993] [drm] Initialized nouveau 1.3.1 20120801 for 0000:01:00.0 on minor 0

[ 2.425203] Guest personality initialized and is inactive

[ 2.425266] VMCI host device registered (name=vmci, major=10, minor=62)

[ 2.425274] Initialized host personality