boot – Does a working nomodeset means the gpu isn’t defective?

I have an M6600 which runs Kubuntu 20.04. I have problems with the screen sometimes. The laptop boots and I am able to log in. After some while I get a brownish display with vertical stripes. Sometimes it doesn’t show the login screen.

What always works is setting nomodeset in grub. Does this mean my problem is software related? I want to check first before I buy a gpu (even the M6600 gpus are quite expensive right now).

Here is some more information about the M6600:

  Host: Precision-M6600 Kernel: 5.8.0-48-generic x86_64 
  bits: 64 Desktop: KDE Plasma 5 
  Distro: Ubuntu 20.10 (Groovy Gorilla) 
  Type: Laptop System: Dell product: Precision M6600 v: 01 
  serial: <superuser/root required> 
  Mobo: Dell model: 04YY4M v: A00 
  serial: <superuser/root required> BIOS: Dell v: A04 
  date: 07/11/2011 
  ID-1: BAT0 charge: 86.9 Wh condition: 86.9/98.2 Wh (88%) 
  Info: Dual Core Intel Core i5-2520M (MT MCP) speed: 2394 MHz 
  min/max: 800/3200 MHz 
  Device-1: AMD Blackcomb (Radeon HD 6970M/6990M) driver: N/A 
  Device-2: Ricoh type: USB driver: uvcvideo 
  Display: x11 server: 1.20.9 driver: vesa FAILED: ati 
  unloaded: fbdev,modesetting,radeon 
  Message: No advanced graphics data found on this system. 
  Device-1: Intel 82579LM Gigabit Network driver: e1000e 
  Device-2: Intel Centrino Ultimate-N 6300 driver: iwlwifi 
  Local Storage: total: 592.27 GiB used: 29.86 GiB (5.0%) 
  Processes: 204 Uptime: 22m Memory: 7.73 GiB 
  used: 1.48 GiB (19.1%) Shell: Bash inxi: 3.1.07