MacOS – GPU-defect Macbook Pro 2011 does not accept csrutil disable anymore (10.13.6)

Since people are still commenting on this, I will post what happened as my answer: I took the MBP to a different store where they concluded that it was a faulty HDD cable since I had installed the SSD myself and they assumed it got some kind of shock for me not wearing an ESD bracelet. (Although as far as I can remember, the friend of mine who installed the SSD for me did indeed wear the bracelet, however I probably didn't use it when I installed RAM 1,5 years ago)

It seemed to work fine for a while but after that, the glitches started to reappear, and it became so bad that the MBP couldn't boot into OS X or Windows (stuck on grey screen with glitchy stripes).

Once again, I took it to the shop, they concluded that it was a faulty logic board, which would cost me a fortune to replace. However, thanks to EU consumer laws, I have the right of up to 3 years warranty if I could prove that it's the manufacturer's fault. So they let me fill in a form and send it in along with my receipt. By the beginning of July, Apple finally approved to replace the logic board for free. For now, the MBP is working properly again.

No, you most likely have the very same common GPU issue. Seeing the glitches multiple times is a sure tell sign.

Beneath all that drama caused by resetting and tweaking things, temperature variations on the GPU contacts were what caused the glitches and the inconsistent behaviors. Your laptop is probably in the initial phase of GPU(soldering) failure. Sooner or later the problem worsens and more severe graphic glitches will appear or the computer simply becomes unbootable.

You can try the simple steps below to stress-test the GPU, but by doing so you could be accelerating the problem and end up in an unusable state sooner. You can decide if it's in your interest to forcefully trigger the problem. Regardless, these steps are not beyond any normal operating parameters, so if your laptop is immune from the GPU problem you are not doing anything harmful by performing these steps, warranty-wise especially.

1. Get a temperature & fan speed monitoring app like iStat Menus that can show you fan speeds, CPU and GPU temperatures in real time.

2. Run a GPU benchmark app to stress the GPU. Valley or Heaven should work, for free. Keep running/looping so the GPU temperature stays around 70'C or higher, for as long as possible (hours).

3. You should pause the benchmark app periodically for the temperature to drop down (back to 45~50'C range). Or just turn it off at nights. Repeat the heating/cooling process until the symptoms appear.

This test might end up proving nothing, and yet it doesn't mean the GPU is trouble-free. It takes time and many temperature cycles for the solder joint problem to become apparent.