Hi!
Yeah, I recognize this issue and it's not good.
Your GPU is probably dying and as it's hard (almost impossible) find the GPU chip, you probably do need to replace the motherboard to get this fixed.... Is it modded with a modchip? If yes, please remove this first to see if it's solved or not. Probably this won't solve it, so a motherboard replacement is required. Motherboards are also very hard to find.. So you can buy a donor-broken motherboard with other issues, so you can take the component of it. This is very hard and you do need solder experience.
Sorry for the bad news...