Ensure you installed Audacity correctly and are not running it from the DMG: https://forum.audacityteam.org/t/installation-do-not-run-audacity-from-the-dmg/31711/1
If that does not help, it is probably Gatekeeper interfering, so you will need to do the following: Open /Applications/Utilities/Terminal.app. Copy the below text then paste it into the terminal:
sudo xattr -r -d com.apple.quarantine /Applications/Audacity/
Hit ENTER to send the command. Type the admin password when prompted. You won’t see the password while typing it, but hit ENTER when you have finished typing it.
Then reboot.
If Audacity is installed somewhere else than /Applications/Audacity, change the path to reflect where the Audacity folder is.