Audacity should be attempting to write to /User//Library/Application Support/audacity/SessionData/
Please check in Audacity > Preferences > Directories that this is the location of the temporary files.
If not, use the “Choose” button to navigate to the SessionData folder and choose it as the temp files location. If the folder does not exist, create it.
If the “audacity” folder does not exist inside “Application Support”, please follow the instruction in this forum post to reset your Audacity settings. You only need to delete the “audacity.cfg” file. You do not need to delete the “pluginsettings” and “pluginregistry” files.
– Bill