OK!! I have had the issue of getting "error code 999 and GPU memory full" using DaVinci Resolve Studio on my hybrid graphics laptop running Linux for A YEAR now!!! Finally found a solution via Reddit and it's to launch resolve using this command:
__NV_PRIME_RENDER_OFFLOAD=1 __GLX_VENDOR_LIBRARY_NAME=nvidia /opt/resolve/bin/resolve
It works fine now so far!! Hope anyone else with this problem finds it useful! I am not a Terminal junky and try to do everything via a GUI but at least it works now!