GPU disable on boot was successful for months – but cannot execute sh /force-iGPU-boot.sh anymore from Single User Mode
I would suggest disabling SIP (System Integrity Protection) by rebooting your laptop into Recovery Mode by holding down Cmd+R while booting, and then opening the Terminal and running the following command:
csrutil disable

Now close the Terminal window and reboot into single-user mode, and try your commands again.