We don’t make Audacity 2.1 - all our versions have three numbers. Make sure you obtain Audacity 2.1.0 from us here http://web.audacityteam.org/download/mac.
Make sure you are installing Audacity properly according to these instructions: https://forum.audacityteam.org/t/installation-do-not-run-audacity-from-the-dmg/31711/1 If you are running Audacity from the DMG you will have all sort of issues.
If that does not help, look at Audacity > Preferences… then the “Directories” section. Choose a temp directory that you have permission to write to and that has sufficient space (hundreds of GB if your tracks are over an hour long).
Gale