GPU disable on boot was successful for months – but cannot execute sh /force-iGPU-boot.sh anymore from Single User Mode

I had this common GPU issue on a 2011 MBP that I was able to solve with the super detailed post by the user "LаngLаngС" (thanks so much!) as found at
GPU problem – Boot Hangs on Grey Screen.

Unfortunately, a new issue has arisen that prevents me from running the script. I’ll explain:

To solve the GPU issue I everything as written in LangLangC’s post and I also had the executable sh script on my desktop—so when I had to boot the Mac again, I did this in single user mode with CMD + Sand then typed sh /force-iGPU-boot.sh and then reboot. This would boot my machine always as normal with the internal GPU.

So far, so good—until yesterday.

• When trying to reboot again from Single User Mode, I got this new prefix "sh 3.2#" and the lines looked different. It says that the volume is "read only".

• When I try to execute sh /force-iGPU-boot.shit says, "file or directory not found".

• I can’t run sudo commands as it says "command not found".

• When I try to remount with mount -uwit doesn’t work – it always says "device is write locked".

When I type exit or reboot, the system actually seems to boot "normal"if there wasn’t the GPU issue! Meaning that if I cannot run the script "force-iGPU-boot.sh" from the single user mode, I cannot boot the GUI Mac OSX properly. Unfortunately, I also cannot execute the sudo commands. I also tried to boot the Mac in target mode and "repair" the drive with the disk utility of another Mac, but that never worked either.

I was googling a lot and tried a lot, but nothing worked yet. Since I am not very familiar with these kinds of issues, I was hoping to find an answer here, where I found the first answers to my GPU problem.

Basically, my "new problem" is that I cannot run the automated script that I saved on the desktop or the sudo commands from the single-user mode.

This is the output of sw_vers:

while in single-user mode.
    $ /sbin/fsck -fy
    $ /sbin/mount -uw /
To boot the system:
    $ exit
-sh-32.# sw_vers
ProductName:     Mac OS X
Product Version: 10.13.6
BuildVersion:    17G14033
-sh-32#

Is anyone able to offer a suggestion to run this script?