Quit DaVinci Resolve
The switch is read when Resolve loads the plugins. Save your project and quit the app before changing it.
Create the CPU-only flag
Run the following two commands in Terminal, then reopen Resolve. These commands create a folder if needed and an empty flag file; they do not alter your projects.
mkdir -p "$HOME/Library/Application Support/Paperwolf Studio"
touch "$HOME/Library/Application Support/Paperwolf Studio/cpu-only"Return to GPU rendering
Quit Resolve. In Finder choose Go → Go to Folder and paste ~/Library/Application Support/Paperwolf Studio/. Move only the file named cpu-only to the Trash, then reopen Resolve. Leave licences and other files in place.
Still having trouble?
Record your Mac model, macOS version, Resolve version, plugin and look name, and whether the issue also occurs on CPU.