OK, I hope I fixed it for now via revision 5:
nvidia-driver-assistant --simulate-gpu 750 --verbose
DEBUG:root:get_nvidia_devices(): Processing Vendor: 10DE, Device ID: 0x1380, class 0x0300
DEBUG:root:pci:v000010DEd00001380sv000010DEsd000018FEbc03sc00i00
DEBUG:root:Device: has following feature: hdmi4k
DEBUG:root:Device: has following feature: vdpaufeaturesete
DEBUG:root:Device: has following flags: []
DEBUG:root:Device: needs proprietary driver
DEBUG:root:gpu.get(legacybranch): NVIDIA GeForce GTX 750 Ti belongs to legacybranch = 580.xx
Detected GPUs:
NVIDIA GeForce GTX 750 Ti - (pci_id 0x1380)
DEBUG:root:recommend_driver(): Do device IDs support the open driver?
DEBUG:root:recommend_driver(): using json logic
DEBUG:root:recommend_driver(): all devices require closed
DEBUG:root:Recommended driver: closed
DEBUG:root:get_distro(): detected manjaro distribution is supported
Detected system:
Manjaro Linux
DEBUG:root:OS detected: manjaro
DEBUG:root:get_legacy_branch(): NVIDIA GeForce GTX 750 Ti belongs to legacybranch = 580.xx
Please copy and paste the following command to install the legacy kernel module flavour:
sudo pacman -S linux618-nvidia-580xx