OK, maybe you didn’t build and install the packages properly? Not enough explanation to me. Do we just trust you did it right or can you provide exactly what you did? (//EDIT: here is proper way [HowTo] get legacy 340xx NVIDIA drivers back originally from here [Support/How-To] Compile old/legacy Nvidia Proprietary Drivers [2020-12-30 Update Issue] with more details)
And also I forgot, here is how to provide information about your machine: How to provide good information